0000950170-24-052678 | 10-Q | XBRL Viewer

Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2024

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Summary of Status and Activity of Non-Vested Stock Units

The following table shows a summary of the status and activity of non-vested stock units:


	Restricted Stock Units			Performance Stock Units			Total Stock Units			Weighted Average Grant Date Fair Value per Unit
Non-vested at December 31, 2023		531,339			580,763			1,112,102		$	33.62
Granted		145,627			182,196			327,823		$	48.95
Credited from dividends		170			0			170		$	43.00
Vested		(209,723	)		(136,560	)		(346,283	)	$	32.83
Forfeited		(4,239	)		(2,198	)		(6,437	)	$	31.91
Non-vested at March 31, 2024		463,174			624,201			1,087,375		$	38.50

Summary of Status and Activity of Stock Options

The following table shows a summary of the status and activity of stock options:


	Options			Weighted Average Exercise Price per Option		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2023		706,868		$	27.51
Exercised		(132,131	)	$	26.78
Outstanding at March 31, 2024		574,737		$	27.67		4.84	$	15.8
Exercisable at March 31, 2024		502,962		$	27.14		4.46	$	14.1

Schedule of Stock-based Compensation Expense Recognized

The following table presents total stock-based compensation expense recognized in the condensed consolidated statement of operations:


	Three Months Ended March 31,
	2024		2023
(Dollars in millions)
Selling, general and administrative expenses	$	5.4	$	4.0
Less related income tax benefit		1.5		1.1
Decrease in net income attributable to Koppers	$	3.9	$	2.9

Performance Stock Units [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Stock Options And Performance Award Fair Value Assumptions

We calculated the fair value of the performance stock units with a market condition on the date of grant using a Monte Carlo valuation model and the assumptions listed below:


	January 2024 Grant
Grant date price per share of performance award	$	46.68
Expected volatility		38.14	%
Risk-free interest rate		4.14	%
Look-back period in years		3.00
Grant date fair value per share	$	59.41

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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+ Details

Fair Value Measurements

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The following table presents the estimated fair values and the related carrying amounts of our financial instruments:


	March 31, 2024				December 31, 2023
	Fair Value		Carrying Value		Fair Value		Carrying Value
(Dollars in millions)
Financial assets:
Investments and other assets	$	1.3	$	1.3	$	1.3	$	1.3
Financial liabilities:
Long-term debt (including current portion)	$	888.3	$	877.6	$	860.4	$	849.4

Investments and other assets – Represents the broker-quoted cash surrender value on universal life insurance policies. This asset is classified as Level 2 in the valuation hierarchy.

Debt – The fair value of our long-term debt is estimated based on the market prices for the same or similar issuances or on the current rates offered to us for debt of the same remaining maturities (Level 2). The fair value of our Credit Facility (as defined in Note 11 – Debt) approximates carrying value due to the variable rate nature of this instrument.

See Note 12 – Derivative Financial Instruments, for the fair value of our derivative financial instruments.

Commitments and Contingent Liabilities (Tables)

3 Months Ended

Mar. 31, 2024

Commitments and Contingencies Disclosure [Abstract]

Changes in Accrued Liability for Environmental Matters

The following table reflects changes in the accrual for environmental remediation. A total of $2.2 million was classified as current liabilities as of March 31, 2024 and December 31, 2023.


	Period ended
	March 31, 2024			December 31, 2023
(Dollars in millions)
Balance at beginning of period	$	10.6		$	10.9
Expense		0.0			0.2
Cash expenditures		0.0			(0.4	)
Currency translation		(0.1	)		(0.1	)
Balance at end of period	$	10.5		$	10.6

Commitments and Contingent Liabilities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2024 USD ($) Case Site Plant State Plaintiff Party	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Loss Contingencies [Line Items]
Number of states with new claims filed \| State	2
Number of plaintiffs \| Plaintiff	51
Environmental remediation and regulation liability	$ 10,500,000	$ 10,600,000	$ 10,900,000
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]	Liabilities, Current
Accrued liability for environmental matters, current	$ 2,200,000	$ 2,200,000
Environmental Loss Contingency, Current, Statement of Financial Position [Extensible Enumeration]	Liabilities, Current	Liabilities, Current
Portland Harbor and Newark Bay CERCLA sites [Member]
Loss Contingencies [Line Items]
Costs of participating in PRP group	$ 3,900,000
Beazer East [Member]
Loss Contingencies [Line Items]
Sites listed on National Priorities List \| Site	1
Compensatory Damages [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	27
Punitive Damages [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	24
Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	27
Reserve for legal proceedings	$ 0
Pennsylvania [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	26
Pennsylvania [Member] \| Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	26
Sweetwater, Tennessee [Member] \| Coal Tar Pitch Cases [Member]
Loss Contingencies [Line Items]
Number of cases \| Case	1
Compensatory damages	$ 15,000,000.0
Oregon [Member]
Loss Contingencies [Line Items]
Number of potential responsible parties \| Party	80
Net present value of selected remedy estimation	$ 1,100,000,000
Undiscounted cost of selected remedy estimation	1,700,000,000
United States [Member]
Loss Contingencies [Line Items]
Environmental remediation and regulation liability	$ 3,800,000
United States [Member] \| Performance Chemicals [Member]
Loss Contingencies [Line Items]
Number of plant sites \| Plant	2
United States [Member] \| Utility and Industrial Products [Member]
Loss Contingencies [Line Items]
Number of plant sites \| Plant	1
Australia [Member] \| Performance Chemicals [Member]
Loss Contingencies [Line Items]
Environmental remediation and regulation liability	$ 1,200,000

Commitments and Contingent Liabilities - Changes in Accrued Liability for Environmental Matters (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Balance at beginning of period	$ 10.6	$ 10.9
Expense	0.0	0.2
Cash expenditures	0.0	(0.4)
Currency translation	(0.1)	(0.1)
Balance at end of period	$ 10.5	$ 10.6

Inventories, Net

3 Months Ended

Mar. 31, 2024

Inventory Disclosure [Abstract]

Inventories, Net

9. Inventories, net


	March 31, 2024		December 31, 2023
(Dollars in millions)
Raw materials	$	348.4	$	348.4
Work in process		15.8		17.9
Finished goods		147.0		139.0
Total	$	511.2	$	505.3
Less revaluation to LIFO		112.2		109.6
Net	$	399.0	$	395.7

Earnings and Dividends per Common Share (Tables)

3 Months Ended

Mar. 31, 2024

Earnings Per Share [Abstract]

Schedule of Computation of Basic and Diluted Earnings per Common Share

The following table sets forth the computation of basic and diluted earnings per common share:


	Three Months Ended March 31,
	2024		2023
(Dollars in millions, except share and per share amounts)
Net income attributable to Koppers	$	13.0	$	25.5
Weighted average common shares outstanding (in thousands):
Basic		21,066		20,842
Effect of dilutive securities		843		543
Diluted		21,909		21,385
Earnings per common share:
Basic	$	0.61	$	1.22
Diluted		0.59		1.19
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share		55		629

Comprehensive Income (Loss) and Equity - Schedule of Comprehensive Income (Loss) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Equity [Abstract]
Tax (expense) benefit, unrealized gain (loss) on cash flow hedges	$ 2.8	$ 1.9

Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net income	$ 13.0	$ 26.2
Changes in other comprehensive income (loss):
Currency translation adjustment	(13.9)	2.7
Cash flow hedges, net of tax expense of $2.8 and $1.9	7.0	4.7
Pension adjustments, net of tax expense of $0.1 and $0.1	0.4	0.3
Comprehensive income	6.5	33.9
Comprehensive income attributable to noncontrolling interests	0.0	0.7
Comprehensive income attributable to Koppers	$ 6.5	$ 33.2

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income (loss) and other comprehensive income (loss), attributable to noncontrolling interests. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

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+ Details

Subsequent Events

3 Months Ended

Mar. 31, 2024

Subsequent Events [Abstract]

Subsequent Events

14. Subsequent Events

On April 1, 2024, we completed our acquisition of substantially all of the assets of Brown Wood Preserving Company, Inc. and certain of its affiliates (Brown Wood) for approximately $100 million in cash, subject to a post-closing working capital adjustment to be determined. Brown Wood is a utility pole treating business with principal operating locations in Alabama and Mississippi. We financed the acquisition with cash and available borrowings under our Credit Facility.

Basis of Presentation

3 Months Ended

Mar. 31, 2024

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Basis of Presentation

1. Basis of Presentation

The accompanying unaudited condensed consolidated financial statements and related disclosures have been prepared in accordance with accounting principles generally accepted in the United States applicable to interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation of Koppers Holdings Inc.’s and its subsidiaries’ (Koppers, Koppers Holdings, the Company, we or us) financial position and interim results as of and for the periods presented have been included. All such adjustments are of a normal recurring nature unless disclosed otherwise. Because our business is seasonal, results for interim periods are not necessarily indicative of those that may be expected for a full year. The Condensed Consolidated Balance Sheet as of December 31, 2023 has been summarized from the audited balance sheet contained in the Annual Report on Form 10-K as of and for the year ended December 31, 2023. Certain prior period amounts in the condensed consolidated financial statements and notes to the condensed consolidated financial statements have been reclassified to conform to the current period’s presentation.

The financial information included herein should be read in conjunction with our audited consolidated financial statements and related notes included in our Annual Report on Form 10-K for the year ended December 31, 2023.

Leases - Schedule of Supplemental Condensed Consolidated Balance Sheet Information Related to Leases (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Operating leases:
Operating lease right-of-use assets	$ 85.8	$ 90.5
Current operating lease liabilities	22.2	22.9
Operating lease liabilities	$ 63.4	$ 67.4

Debt

3 Months Ended

Mar. 31, 2024

Debt Disclosure [Abstract]

Debt

11. Debt

The following table summarizes debt:


	Weighted Average Interest Rate			Maturity	March 31, 2024		December 31, 2023
(Dollars in millions)
Credit Facility		7.29	%	2027	$	491.3	$	461.4
Term Loan B		8.93	%	2030		386.3		388.0
Debt					$	877.6	$	849.4
Less short-term debt and current maturities of long-term debt						4.0		5.0
Less unamortized debt issuance costs						8.5		9.0
Long-term debt					$	865.1	$	835.4

Credit Facility

We have a credit agreement (the Credit Facility) with a consortium of banks. The Credit Facility provides for an $800.0 million revolving credit facility, a $50.0 million swingline facility and provides for the ability to incur one or more uncommitted incremental revolving or term loan facilities in an aggregate amount of at least $730.0 million, subject to applicable financial covenants. The interest rate on the Credit Facility is variable and may be based on the Secured Overnight Financing Rate (SOFR), which is the applicable benchmark for current borrowings, or an alternative benchmark depending on the borrowing type.

Borrowings under the Credit Facility are secured by a first priority lien on substantially all of the assets (excluding real property and other customary assets) of Koppers Inc., Koppers Holdings Inc. and our material domestic subsidiaries. The Credit Facility contains certain covenants that may limit Koppers Inc. and its restricted subsidiaries from taking certain actions. These limitations include, among others, restrictions on additional indebtedness, liens, dividends, investments, acquisitions, certain distributions, asset sales, transactions with affiliates and modifications to material documents, including organizational documents. In addition, such covenants may give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios.

As of March 31, 2024, we had approximately $301 million of unused revolving credit availability after restrictions from certain letter of credit commitments and other covenants. As of March 31, 2024, $7.8 million of commitments were utilized by outstanding letters of credit.

Term Loan B

In April 2023, a new class of senior secured term loans under the Credit Facility (the Term Loan B) was issued at 97 percent of face value, resulting in $388.0 million of net proceeds, before debt financing costs. The interest rate on the Term Loan B is variable and is based on, at our option, adjusted Term SOFR Rate or adjusted Daily Simple SOFR. The interest rate margins applicable to adjusted Term SOFR Rate or adjusted Daily Simple SOFR loans are 3.50 percent with a floor of 0.50 percent. The principal balance of the Term Loan B is repayable in quarterly installments in an amount equal to 0.25 percent of the principal amount, commencing on January 1, 2024 and on the last business day of each quarterly period thereafter, with the balance due at maturity on April 10, 2030.

Interest Rate Swaps

See Note 12 – Derivative Financial Instruments for discussion of the interest rate swap agreements, which effectively convert the variable rate to a fixed rate for a portion of our variable rate debt.

Subsequent Events

On April 12, 2024, we entered into Amendment No. 3 to the Credit Facility (Amendment No. 3) which, among other modifications: (i) provides for the incurrence of incremental term loans in an aggregate principal amount of $100 million to be used for general corporate purposes, thereby increasing the aggregate principal amount of the Term Loan B to $497 million as of April 12, 2024 and (ii) effectively reduces the interest rate margins applicable to the Term Loan B by 0.50 percent to 3.00 percent with a floor of 0.50 percent, in the case of adjusted Term SOFR Rate or adjusted Daily Simple SOFR loans.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

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+ Details

Segment Information (Tables)

3 Months Ended

Mar. 31, 2024

Segment Reporting [Abstract]

Schedule of Segment Revenues for Significant Product Lines

The following table sets forth revenues for significant product lines, net of all intersegment transactions, for our segments:


	Three Months Ended March 31,
	2024		2023
(Dollars in millions)
Railroad and Utility Products and Services:
Railroad treated products	$	141.9	$	127.5
Utility poles		64.5		63.3
Railroad infrastructure products and services		18.7		22.3
Total Railroad and Utility Products and Services		225.1		213.1
Performance Chemicals:
Wood preservative products		141.1		136.9
Other products		9.0		10.0
Total Performance Chemicals		150.1		146.9
Carbon Materials and Chemicals:
Pitch and related products		72.8		105.8
Phthalic anhydride, naphthalene, and other chemicals		34.6		29.0
Carbon black feedstock and distillates		15.0		18.6
Total Carbon Materials and Chemicals		122.4		153.4
Total	$	497.6	$	513.4
Intersegment revenues:
Performance Chemicals	$	7.6	$	5.6
Carbon Materials and Chemicals		26.3		19.0
Total	$	33.9	$	24.6

Summary of Results of Segment Operations

The following table sets forth certain operating data, net of all intersegment transactions, for our segments:


	Three Months Ended March 31,
	2024			2023
(Dollars in millions)
Depreciation and amortization expense:
Railroad and Utility Products and Services	$	6.9		$	5.9
Performance Chemicals		3.4			3.5
Carbon Materials and Chemicals		5.8			4.6
Total	$	16.1		$	14.0
Adjusted EBITDA:
Railroad and Utility Products and Services	$	17.7		$	15.8
Performance Chemicals		29.8			26.3
Carbon Materials and Chemicals		4.0			19.4
Items excluded from the determination of segment profit:
LIFO expense(1)		(2.6	)		(0.3	)
Gain on sale of assets		0.0			1.8
Mark-to-market commodity hedging gains		1.7			1.1
Interest expense		(17.1	)		(14.0	)
Depreciation and amortization		(16.1	)		(14.0	)
Income tax provision		(4.4	)		(9.9	)
Net income	$	13.0		$	26.2

(1)

The LIFO expense adjustment removes the entire impact of LIFO and effectively reflects the results as if we were on a FIFO inventory basis.

Summary of Assets and Goodwill by Segments

The following table sets forth assets and goodwill allocated to each of our segments:


	March 31, 2024		December 31, 2023
(Dollars in millions)
Segment assets:
Railroad and Utility Products and Services	$	759.3	$	743.7
Performance Chemicals		530.9		520.6
Carbon Materials and Chemicals		516.4		538.9
All other		38.7		32.3
Total	$	1,845.3	$	1,835.5
Goodwill:
Railroad and Utility Products and Services	$	120.5	$	120.6
Performance Chemicals		172.6		173.8
Total	$	293.1	$	294.4

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income taxes as a percentage of pretax income	25.30%	27.40%
Estimated annual effective income tax rate	28.30%	28.40%
Unrecognized tax benefits	$ 1.5		$ 1.5
Minimum effective corporate tax rate income as per pillar two	15.00%

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Millions	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ 13.0	$ 25.5

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

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-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

+ Details

Condensed Consolidated Statement of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash provided by (used in) operating activities:
Net income	$ 13.0	$ 26.2
Adjustments to reconcile net cash used in operating activities:
Depreciation and amortization	16.1	14.0
Stock-based compensation	5.4	4.0
Change in derivative contracts	(1.8)	(1.1)
Non-cash interest expense	0.8	0.6
Loss (gain) on sale of assets	0.1	(1.8)
Insurance proceeds	(0.5)	0.0
Deferred income taxes	0.5	(0.1)
Change in other liabilities	(3.8)	0.4
Other - net	(0.8)	0.4
Changes in working capital:
Accounts receivable	(18.2)	(25.1)
Inventories	(8.2)	(22.4)
Accounts payable	(4.3)	14.1
Accrued liabilities	(9.0)	(18.5)
Other working capital	(1.6)	(6.0)
Net cash (used in) operating activities	(12.3)	(15.3)
Cash (used in) provided by investing activities:
Capital expenditures	(26.3)	(30.4)
Insurance proceeds received	0.5	0.0
Cash provided by sale of assets	0.0	1.9
Net cash (used in) investing activities	(25.8)	(28.5)
Cash provided by (used in) financing activities:
Borrowings of credit facility	190.7	122.0
Repayments of credit facility	(160.8)	(58.5)
Repayments of long-term debt	(2.0)	0.0
Issuances of Common Stock	3.5	1.2
Repurchases of Common Stock	(6.9)	(5.8)
Payment of debt issuance costs	0.0	(0.8)
Dividends paid	(1.5)	(1.3)
Net cash provided by financing activities	23.0	56.8
Effect of exchange rate changes on cash	(2.4)	0.1
Net (decrease) increase in cash and cash equivalents	(17.5)	13.1
Cash and cash equivalents at beginning of period	66.5	33.3
Cash and cash equivalents at end of period	49.0	46.4
Supplemental disclosure of non-cash investing and financing activities:
Right-of-use assets obtained in exchange for new operating lease liabilities	1.8	5.9
Accrued capital expenditures	$ 3.5	$ 8.4

Inventories, Net (Tables)

3 Months Ended

Mar. 31, 2024

Inventory Disclosure [Abstract]

Components of Net Inventories


	March 31, 2024		December 31, 2023
(Dollars in millions)
Raw materials	$	348.4	$	348.4
Work in process		15.8		17.9
Finished goods		147.0		139.0
Total	$	511.2	$	505.3
Less revaluation to LIFO		112.2		109.6
Net	$	399.0	$	395.7

Pensions and Post-Retirement Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss		$ 20.0
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Premium payment		$ 67.8
US Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Additional Cash Funding	$ 25.0
Pension settlement loss	$ 40.0

Condensed Consolidated Statement of Operations - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Statement [Abstract]
Net sales	$ 497.6	$ 513.4
Cost of sales	401.4	409.3
Depreciation and amortization	16.1	14.0
Selling, general and administrative expenses	45.5	41.6
(Gain) on sale of assets	0.0	(1.8)
Operating profit	34.6	50.3
Other loss, net	(0.1)	(0.2)
Interest expense	17.1	14.0
Income before income taxes	17.4	36.1
Income tax provision	4.4	9.9
Net income	13.0	26.2
Net income attributable to noncontrolling interests	0.0	0.7
Net income attributable to Koppers	$ 13.0	$ 25.5
Earnings per common share attributable to Koppers common shareholders:
Basic	$ 0.61	$ 1.22
Diluted	$ 0.59	$ 1.19
Weighted average shares outstanding (in thousands):
Basic	21,066	20,842
Diluted	21,909	21,385

Derivative Financial Instruments - Schedule of Outstanding Copper Swap Contracts (Detail) - Copper Swap Contracts [Member] £ in Millions, $ in Millions	Mar. 31, 2024 GBP (£)	Mar. 31, 2024 USD ($)	Dec. 31, 2023 GBP (£)	Dec. 31, 2023 USD ($)
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding \| £	£ 37.2		£ 41.2
Net Fair Value - Asset \| $		$ 8.8		$ 4.1
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding \| £	26.6		31.7
Net Fair Value - Asset \| $		5.8		2.6
Contracts Where Hedge Accounting Was not Elected [Member]
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding \| £	£ 10.6		£ 9.5
Net Fair Value - Asset \| $		$ 3.0		$ 1.5

- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References + Details

Condensed Consolidated Statement of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Tax expense, cash flow hedges, net	$ 2.8	$ 1.9
Tax expense, pension adjustments, net	$ 0.1	$ 0.1

Segment Information - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) Segment	Dec. 31, 2023 USD ($)
Segment Reporting [Abstract]
Number of reportable segments \| Segment	3
Contract with customer, asset, net, current \| $	$ 5.1	$ 7.8

Income Taxes

3 Months Ended

Mar. 31, 2024

Income Tax Disclosure [Abstract]

Income Taxes

8. Income Taxes

Effective Tax Rate

The income tax provision for interim periods is comprised of an estimated annual effective income tax rate applied to current year ordinary income and tax associated with discrete items. These discrete items generally relate to excess stock compensation deductions, changes in tax laws, adjustments to unrecognized tax benefits and changes of estimated tax liability to the actual liability determined upon filing income tax returns. To determine the annual effective tax rate, management is required to make estimates of annual pretax income in each domestic and foreign jurisdiction in which we conduct business. Entities that have historical pre-tax losses and current year estimated pre-tax losses that are not projected to generate a future benefit are excluded from the estimated annual effective income tax rate.

The estimated annual effective income tax rate differs from the U.S. federal statutory tax rate due to:


	March 31,
	2024			2023
Federal income tax rate		21.0	%		21.0	%
Foreign earnings taxed at different rates		4.3			4.3
Nondeductible expenses		1.8			1.4
State income taxes, net of federal tax benefit		1.1			1.3
Change in tax contingency reserves		0.1			0.0
GILTI inclusion, net of foreign tax credits		0.0			0.4
Estimated annual effective income tax rate		28.3	%		28.4	%

Income taxes as a percentage of pretax income were 25.3 percent and 27.4 percent for the three months ended March 31, 2024 and 2023, respectively. Both periods were lower than the estimated annual effective income tax rate of 28.3 percent and 28.4 percent due to discrete items, principally an excess tax deduction for vested stock awards.

During the year, management regularly updates estimates of pre-tax income and income tax expense based on changes in pre-tax income projections by taxable jurisdiction, repatriation of foreign earnings, unrecognized tax benefits and other tax matters. Effective January 1, 2024, certain jurisdictions in which we operate have enacted legislation that is consistent with one or more Organization for Economic Co-operation and Development Global Anti-Base Erosion Model Rules (commonly referred to as "Pillar Two"). These Pillar Two rules include minimum domestic top up taxes, income inclusion rules and undertaxed profit rules all aimed to ensure that multinationals pay a minimum effective corporate tax rate of 15 percent in each jurisdiction in which they operate. We do not expect these Pillar Two rules to materially impact our annual effective rate in 2024. To the extent that actual results vary from these estimates, the actual annual effective income tax rate at the end of the year could be materially different from the estimated annual effective income tax rate for the three months ended March 31, 2024.

Unrecognized Tax Benefits

We file income tax returns in the U.S. federal jurisdiction, individual U.S. state jurisdictions and non-U.S. jurisdictions. With few exceptions, we are no longer subject to U.S. federal, U.S. state, or non-U.S. income tax examinations by tax authorities for years prior to 2017.

As of March 31, 2024 and December 31, 2023, unrecognized tax benefits of $1.5 million for both periods would affect the effective tax rate if recognized. We do not anticipate material changes to the amount of unrecognized tax benefits within the next twelve months.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Segment Information - Schedule of Segment Revenues for Significant Product Lines (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Net sales	$ 497.6	$ 513.4
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Net sales	33.9	24.6
Railroad and Utility Products and Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	225.1	213.1
Railroad and Utility Products and Services [Member] \| Railroad Treated Products [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	141.9	127.5
Railroad and Utility Products and Services [Member] \| Utility Poles [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	64.5	63.3
Railroad and Utility Products and Services [Member] \| Railroad Infrastructure Products and Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	18.7	22.3
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	150.1	146.9
Performance Chemicals [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Net sales	7.6	5.6
Performance Chemicals [Member] \| Wood Preservative Products [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	141.1	136.9
Performance Chemicals [Member] \| Other Products [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	9.0
Carbon Materials and Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	122.4	153.4
Carbon Materials and Chemicals [Member] \| Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Net sales	26.3	19.0
Carbon Materials and Chemicals [Member] \| Other Products [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales		10.0
Carbon Materials and Chemicals [Member] \| Pitch and Related Products [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	72.8	105.8
Carbon Materials and Chemicals [Member] \| Phthalic Anhydride, Naphthalene and Other Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	34.6	29.0
Carbon Materials and Chemicals [Member] \| Carbon Black Feedstock and Distillates [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	$ 15.0	$ 18.6

Condensed Consolidated Statement of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Common Stock dividends	$ 0.07	$ 0.06
Amounts reclassified from accumulated other comprehensive income to net income related to derivative financial instruments, net of tax	$ 1.1	$ 1.7

Common Stock (Tables)

9 Months Ended

Sep. 30, 2023

Equity [Abstract]

Schedule of Changes in Common Stock and Treasury Stock

The following table presents changes in common stock and treasury stock:


	Three Months Ended March 31,
	2024			2023
(Shares in thousands)
Common Stock:
Balance at beginning of period		25,163			24,547
Issued for employee stock plans		467			238
Balance at end of period		25,630			24,785
Treasury Stock:
Balance at beginning of period		(4,303	)		(3,784	)
Shares repurchased		(139	)		(178	)
Balance at end of period		(4,442	)		(3,962	)
Common Stock Outstanding		21,188			20,823

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

+ References

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+ Details

Segment Information

3 Months Ended

Mar. 31, 2024

Segment Reporting [Abstract]

Segment Information

7. Segment Information

We have three reportable segments: Railroad and Utility Products and Services (RUPS), Performance Chemicals (PC) and Carbon Materials and Chemicals (CMC). Our reportable segments contain multiple aggregated business units since management believes the long-term financial performance of these business units is affected by similar economic conditions. The reportable segments are each managed separately because they manufacture and distribute distinct products with different production processes.

Our RUPS segment primarily sells pressure-treated railroad ties to the railroad industry and treated utility poles to utility markets. Railroad products and services include procuring and treating items such as crossties, switch ties and various types of lumber used for railroad bridges and crossings. Utility products include the pressure treatment of transmission and distribution poles for electric and telephone utilities. In addition, we provide untreated wood products and rail joint bars, which are steel bars used to join rails together for railroads, to the railroad markets and inspection services to the utility markets. We also operate a railroad services business that conducts engineering, design, repair and inspection services for railroad bridges and a business related to the recovery of used crossties, serving the same customer base as our North American railroad business.

Our PC segment develops, manufactures, and markets wood preservation chemicals and wood treatment technologies and services to a diverse range of end-markets including residential, infrastructure and commercial construction, and agriculture.

Our CMC segment is primarily a manufacturer of creosote, carbon pitch, naphthalene, phthalic anhydride and carbon black feedstock. Creosote is used in the treatment of wood and carbon black feedstock is used in the production of carbon black. Carbon pitch is a critical raw material used in the production of aluminum and steel. Naphthalene is used for the production of phthalic anhydride and as a surfactant in the production of concrete. Phthalic anhydride is used in the production of plasticizers, polyester resins and alkyd paints.

Our primary measure of segment profitability is adjusted earnings before interest, income taxes, depreciation, amortization and certain non-cash and/or non-recurring items that do not contribute directly to management’s evaluation of our operating results (as defined by us, adjusted EBITDA). These items include impairment, restructuring and plant closure costs, mark-to-market commodity hedging, gain or loss on sale of assets and LIFO inventory effects. This presentation is consistent with how our chief operating decision maker evaluates the results of operations and makes strategic decisions about the business. In addition, adjusted EBITDA is the primary measure used to determine the level of achievement of management’s short-term incentive goals and related payout, as well as one of the measures used to determine performance and related payouts for certain performance share units granted to management. For these reasons, we believe that adjusted EBITDA represents the most relevant measure of segment profit and loss.

Adjusted EBITDA is reconciled to net income on a consolidated basis, the most directly comparable financial measure determined and reported in accordance with U.S. GAAP. The accounting policies of the reportable segments are the same as those described in the summary of significant accounting policies. Intersegment transactions are eliminated in consolidation.

Contract Balances

The timing of revenue recognition results in both billed accounts receivable and unbilled receivables, both classified as accounts receivable, net of allowance within the condensed consolidated balance sheet. Contract assets of $5.1 million and $7.8 million are recorded within accounts receivable, net of allowance within the condensed consolidated balance sheet as of March 31, 2024 and December 31, 2023, respectively.

The following table sets forth revenues for significant product lines, net of all intersegment transactions, for our segments:


	Three Months Ended March 31,
	2024		2023
(Dollars in millions)
Railroad and Utility Products and Services:
Railroad treated products	$	141.9	$	127.5
Utility poles		64.5		63.3
Railroad infrastructure products and services		18.7		22.3
Total Railroad and Utility Products and Services		225.1		213.1
Performance Chemicals:
Wood preservative products		141.1		136.9
Other products		9.0		10.0
Total Performance Chemicals		150.1		146.9
Carbon Materials and Chemicals:
Pitch and related products		72.8		105.8
Phthalic anhydride, naphthalene, and other chemicals		34.6		29.0
Carbon black feedstock and distillates		15.0		18.6
Total Carbon Materials and Chemicals		122.4		153.4
Total	$	497.6	$	513.4
Intersegment revenues:
Performance Chemicals	$	7.6	$	5.6
Carbon Materials and Chemicals		26.3		19.0
Total	$	33.9	$	24.6

The following table sets forth certain operating data, net of all intersegment transactions, for our segments:


	Three Months Ended March 31,
	2024			2023
(Dollars in millions)
Depreciation and amortization expense:
Railroad and Utility Products and Services	$	6.9		$	5.9
Performance Chemicals		3.4			3.5
Carbon Materials and Chemicals		5.8			4.6
Total	$	16.1		$	14.0
Adjusted EBITDA:
Railroad and Utility Products and Services	$	17.7		$	15.8
Performance Chemicals		29.8			26.3
Carbon Materials and Chemicals		4.0			19.4
Items excluded from the determination of segment profit:
LIFO expense(1)		(2.6	)		(0.3	)
Gain on sale of assets		0.0			1.8
Mark-to-market commodity hedging gains		1.7			1.1
Interest expense		(17.1	)		(14.0	)
Depreciation and amortization		(16.1	)		(14.0	)
Income tax provision		(4.4	)		(9.9	)
Net income	$	13.0		$	26.2

(1)

The LIFO expense adjustment removes the entire impact of LIFO and effectively reflects the results as if we were on a FIFO inventory basis.

The following table sets forth assets and goodwill allocated to each of our segments:


	March 31, 2024		December 31, 2023
(Dollars in millions)
Segment assets:
Railroad and Utility Products and Services	$	759.3	$	743.7
Performance Chemicals		530.9		520.6
Carbon Materials and Chemicals		516.4		538.9
All other		38.7		32.3
Total	$	1,845.3	$	1,835.5
Goodwill:
Railroad and Utility Products and Services	$	120.5	$	120.6
Performance Chemicals		172.6		173.8
Total	$	293.1	$	294.4

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-15

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 40
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-40

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//280/tableOfContent

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 26
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-26

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 34
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-34

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-41

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-21

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-21

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

+ Details

Plant Closure and Divestitures - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Restructuring Cost and Reserve [Line Items]
Gain on sale	$ 0.0	$ 1.8

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Debt - Schedule of Long-Term Debt Instruments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Debt	$ 877.6	$ 849.4
Less short-term debt and current maturities of long-term debt	4.0	5.0
Less unamortized debt issuance costs	8.5	9.0
Long-term debt	$ 865.1	835.4
Term Loan B [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	8.93%
Debt, Maturity	2030
Debt	$ 386.3	388.0
7.29 Percent Credit Facility [Member] \| Credit Facility [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	7.29%
Debt, Maturity	2027
Debt	$ 491.3	$ 461.4

Subsequent Events - Additional Information (Detail) $ in Millions	Apr. 01, 2024 USD ($)
Subsequent Event [Member] \| Brown Wood Preserving Company, Inc [Member]
Subsequent Event [Line Items]
Value of the assets acquired	$ 100

Stock-based Compensation - Performance Award Fair Value Assumptions (Detail) - January 2024 Grant [Member] - Performance Stock Units [Member]	3 Months Ended
	Mar. 31, 2024 $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of performance award	$ 46.68
Expected volatility	38.14%
Risk-free interest rate	4.14%
Look-back period in years	3 years
Grant date fair value per share	$ 59.41

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Fair Value Measurements - Schedule of Company's Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value [Member]
Financial assets:
Investments and other assets	$ 1.3	$ 1.3
Financial liabilities:
Long-term debt (including current portion)	888.3	860.4
Carrying Value [Member]
Financial assets:
Investments and other assets	1.3	1.3
Financial liabilities:
Long-term debt (including current portion)	$ 877.6	$ 849.4

Income Taxes (Tables)

3 Months Ended

Mar. 31, 2024

Income Tax Disclosure [Abstract]

Summary of Income Taxes Reconciled with Federal Statutory Rate

The estimated annual effective income tax rate differs from the U.S. federal statutory tax rate due to:


	March 31,
	2024			2023
Federal income tax rate		21.0	%		21.0	%
Foreign earnings taxed at different rates		4.3			4.3
Nondeductible expenses		1.8			1.4
State income taxes, net of federal tax benefit		1.1			1.3
Change in tax contingency reserves		0.1			0.0
GILTI inclusion, net of foreign tax credits		0.0			0.4
Estimated annual effective income tax rate		28.3	%		28.4	%

New Accounting Pronouncements (Policies)

3 Months Ended

Mar. 31, 2024

Accounting Changes and Error Corrections [Abstract]

New Accounting Pronouncements

In November 2023, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. This ASU updates reportable segment disclosures by expanding the frequency and extent of segment disclosures. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023, and for interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. The amendments should be applied retrospectively to all prior periods presented in the financial statements. We are currently evaluating this ASU to determine its impact on our disclosures.

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. This ASU updates income tax disclosures by requiring annual disclosures of consistent categories and greater disaggregation of information in the rate reconciliation and income taxes paid disaggregated by jurisdiction. ASU No. 2023-09 is effective for fiscal years beginning after December 15, 2024. Early adoption is permitted. The amendments should be applied on a prospective basis. We are currently evaluating this ASU to determine its impact on our disclosures.

Derivative Financial Instruments - Schedule of Fair Value of Outstanding Derivative Contracts Recorded in Balance Sheet (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Derivative [Line Items]
Net asset (liability) on balance sheet	$ 11.3	$ 0.2
Accumulated other comprehensive gain (loss), net of tax	6.3	(0.9)
Copper Swap Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	8.8	4.1
Accumulated other comprehensive gain (loss), net of tax	4.5	2.0
Heating Oil Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0	(0.3)
Accumulated other comprehensive gain (loss), net of tax	0.0	0.0
Forward Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0	0.1
Accumulated other comprehensive gain (loss), net of tax	0.0	0.0
Interest Rate Swaps [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	2.5	(3.7)
Accumulated other comprehensive gain (loss), net of tax	1.8	(2.9)
Derivative Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	11.4	7.1
Derivative Contracts [Member] \| Copper Swap Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	7.7	4.1
Derivative Contracts [Member] \| Heating Oil Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0	0.0
Derivative Contracts [Member] \| Forward Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0	0.2
Derivative Contracts [Member] \| Interest Rate Swaps [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	3.7	2.8
Other Assets [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	2.4	(6.5)
Other Assets [Member] \| Copper Swap Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	1.1	0.0
Other Assets [Member] \| Heating Oil Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0	0.0
Other Assets [Member] \| Forward Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0	0.0
Other Assets [Member] \| Interest Rate Swaps [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	1.3	(6.5)
Accrued Liabilities [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet		(0.4)
Accrued Liabilities [Member] \| Heating Oil Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet		(0.3)
Accrued Liabilities [Member] \| Forward Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet		(0.1)
Accrued Liabilities [Member] \| Interest Rate Swaps [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet		0.0
Other Long-Term Liabilities [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	(2.5)
Other Long-Term Liabilities [Member] \| Copper Swap Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0	$ 0.0
Other Long-Term Liabilities [Member] \| Heating Oil Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0
Other Long-Term Liabilities [Member] \| Forward Contracts [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	0.0
Other Long-Term Liabilities [Member] \| Interest Rate Swaps [Member]
Derivative [Line Items]
Net asset (liability) on balance sheet	$ (2.5)

Stock-based Compensation - Additional Information (Detail) - shares	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target shares for units	1,087,375	1,112,102
Stock options issued	0
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	3 years
Target shares for units	463,174	531,339
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting performance stock units if minimum performance criteria are not achieved	0
Stock options, term in years	3 years
Target shares for units	624,201	580,763
Performance Stock Units [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target award earned by participants	200.00%
Performance Stock Units [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target award earned by participants	0.00%
Performance Stock Units [Member] \| Target Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target shares for units	125,399
Market Condition Units [Member] \| Target Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target shares for units	56,796

Comprehensive Income (Loss) and Equity - Schedule of Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023
Equity [Abstract]
Net income	$ 13.0	$ 26.2	$ 26.2
Changes in other comprehensive income (loss):
Currency translation adjustment	(13.9)		2.7
Cash flow hedges, net of tax expense of $2.8 and $1.9	7.0		4.7
Comprehensive income	6.5		33.9
Comprehensive income attributable to noncontrolling interests	0.0		0.7
Comprehensive income attributable to Koppers	$ 6.5		$ 33.2

- Definition

+ References + Details

- Definition

+ References + Details

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

+ Details

Common Stock

3 Months Ended

Mar. 31, 2024

Equity [Abstract]

Common Stock

4. Common Stock

The following table presents changes in common stock and treasury stock:


	Three Months Ended March 31,
	2024			2023
(Shares in thousands)
Common Stock:
Balance at beginning of period		25,163			24,547
Issued for employee stock plans		467			238
Balance at end of period		25,630			24,785
Treasury Stock:
Balance at beginning of period		(4,303	)		(3,784	)
Shares repurchased		(139	)		(178	)
Balance at end of period		(4,442	)		(3,962	)
Common Stock Outstanding		21,188			20,823

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Debt (Tables)

3 Months Ended

Mar. 31, 2024

Debt Disclosure [Abstract]

Schedule of Long-Term Debt Instruments

The following table summarizes debt:


	Weighted Average Interest Rate			Maturity	March 31, 2024		December 31, 2023
(Dollars in millions)
Credit Facility		7.29	%	2027	$	491.3	$	461.4
Term Loan B		8.93	%	2030		386.3		388.0
Debt					$	877.6	$	849.4
Less short-term debt and current maturities of long-term debt						4.0		5.0
Less unamortized debt issuance costs						8.5		9.0
Long-term debt					$	865.1	$	835.4

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

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+ Details

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Less accumulated depreciation	$ 479.4	$ 473.2
Net	$ 640.5	$ 631.7

Derivative Financial Instruments

3 Months Ended

Mar. 31, 2024

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Financial Instruments

12. Derivative Financial Instruments

We utilize derivative instruments to manage exposures to risks that have been identified, measured and are capable of being mitigated. The primary risks that we manage by using derivative instruments are commodity price risk associated with copper, fuel oil, foreign currency exchange risk, principally the U.S. dollar, Australian dollar and British pound sterling, and interest rate risk associated with variable rate borrowings. Generally, we enter into master netting arrangements with the counterparties and offset net derivative positions with the same counterparties. Currently, our agreements do not require cash collateral.

The Company recognizes all derivative instruments as either assets or liabilities at fair value on the balance sheet. The derivative instruments are classified as current or noncurrent based upon the expected timing of cash flows and are subject to offset under our master netting arrangements. A derivative instrument's fair value is determined using significant other observable inputs, a Level 2 fair value measurement.

For derivative instruments that are designated and qualify as cash flow hedges, the effective portion of the gain or loss on the derivative is reported as a component of other comprehensive income and is reclassified into earnings in the same period or periods during which the hedged transaction affects earnings. Gains and losses on the derivative instruments representing hedge ineffectiveness are recognized in current earnings.

Swap contracts on copper are used to manage the price risk associated with forecasted purchases of materials used in our manufacturing processes. Generally, we will not hedge cash flow exposures for durations longer than 36 months and we have hedged certain volumes of copper through the end of 2025. We designate certain of our commodity swaps as cash flow hedges of forecasted purchases of commodities. For those commodity swaps where hedge accounting is not elected, the fair value of the commodity swap is recognized as an asset or liability on the condensed consolidated balance sheet and the related unrealized gain or loss on the derivative is reported in current earnings. These amounts are classified in cost of sales in the condensed consolidated statement of operations.

We enter into heating oil swap contracts to manage price risk associated with fuel oil purchases for our plant operations and certain raw material requirements. The fair value associated with these swap contracts are not designated as hedges, and the related unrealized gain or loss on the derivative is reported in current earnings. These amounts are classified in cost of sales in the consolidated statement of operations. As of March 31, 2024 and December 31, 2023, we had contracts totaling 1.7 million and 1.5 million gallons, respectively.

We enter into foreign currency forward contracts to manage foreign currency risk associated with our receivable and payable balances in addition to foreign-denominated sales. The fair value associated with forward contracts related to foreign currency that are not designated as hedges, and the related unrealized gain or loss on the derivative is reported in current earnings. These amounts are classified in cost of sales in the condensed consolidated statement of operations.

We enter into interest rate swaps to effectively convert portions of our variable interest rate debt into fixed rate debt to add stability to interest expense and to manage our exposure to interest rate movements. We entered into interest rate swap agreements with an aggregate notional value of $400.0 million at a weighted average fixed SOFR rate of 3.97 percent for a portion of our variable rate debt. All swap agreements expire in April 2027. The interest rate swaps have been designated as cash flow hedges on interest payments involving the receipt of variable amounts from a counterparty in exchange for us making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount.

See the condensed consolidated statement of comprehensive income and condensed consolidated statement of shareholders' equity for amounts recorded in other comprehensive income and for amounts reclassified from accumulated other comprehensive income into net income.

The fair value of the outstanding derivative contracts recorded in the balance sheet are as follows:


			March 31, 2024
	Copper Swap Contracts		Heating Oil Contracts		Foreign Currency Forward Contracts		Interest Rate Swap Contracts			Total
(Dollars in millions)
Derivative contracts	$	7.7	$	0.0	$	0.0	$	3.7		$	11.4
Other assets		1.1		0.0		0.0		1.3			2.4
Other long-term liabilities		0.0		0.0		0.0		(2.5	)		(2.5	)
Net asset on balance sheet	$	8.8	$	0.0	$	0.0	$	2.5		$	11.3
Accumulated other comprehensive gain, net of tax	$	4.5	$	0.0	$	0.0	$	1.8		$	6.3


			December 31, 2023
	Copper Swap Contracts		Heating Oil Contracts			Foreign Currency Forward Contracts			Interest Rate Swap Contracts			Total
(Dollars in millions)
Derivative contracts	$	4.1	$	0.0		$	0.2		$	2.8		$	7.1
Accrued liabilities		0.0		(0.3	)		(0.1	)		0.0			(0.4	)
Other long-term liabilities		0.0		0.0			0.0			(6.5	)		(6.5	)
Net asset (liability) on balance sheet	$	4.1	$	(0.3	)	$	0.1		$	(3.7	)	$	0.2
Accumulated other comprehensive gain (loss), net of tax	$	2.0	$	0.0		$	0.0		$	(2.9	)	$	(0.9	)

Over the next twelve months, we estimate unrealized gains of $4.2 million for commodity price hedging as well as unrealized gains of $2.8 million for interest rate swaps will be reclassified from accumulated other comprehensive income into earnings.

Copper Swap Contracts

As of the periods presented, we had outstanding copper swap contracts of the following amounts:


	Units Outstanding (in Pounds)				Net Fair Value – Asset
	March 31, 2024		December 31, 2023		March 31, 2024		December 31, 2023
(Amounts in millions)
Cash flow hedges		26.6		31.7	$	5.8	$	2.6
Contracts where hedge accounting was not elected		10.6		9.5		3.0		1.5
Total		37.2		41.2	$	8.8	$	4.1

The unrealized gain from copper swaps contracts where hedge accounting was not elected is as follows:


	Three Months Ended March 31,
	2024		2023
(Dollars in millions)
Gain from contracts where hedge accounting was not elected	$	1.5	$	1.1

Foreign Currency Forward Contracts

The net currency units outstanding for contracts were:


	March 31, 2024		December 31, 2023
(In millions)
United States Dollars		USD 9.0		USD 10.3
British Pound Sterling		GBP 0.9		GBP 0.0
Australian Dollars		AUD 0.0		AUD 3.0

Comprehensive Income (Loss) and Equity - Additional Information (Detail) - $ / shares		3 Months Ended
	May 02, 2024	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income Loss [Line Items]
Quarterly dividend declared per common share		$ 0.07	$ 0.06
Subsequent Event [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Quarterly dividend declared per common share	$ 0.07
Quarterly dividend, declared date	May 02, 2024
Quarterly dividend, payable date	Jun. 10, 2024
Quarterly dividend, payable date of record	May 24, 2024

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Derivative Financial Instruments - Summary of Net Currency Units Outstanding (Detail)	Mar. 31, 2024 AUD ($)	Mar. 31, 2024 GBP (£)	Mar. 31, 2024 USD ($)	Dec. 31, 2023 AUD ($)	Dec. 31, 2023 GBP (£)	Dec. 31, 2023 USD ($)
Offsetting [Abstract]
Net currency units outstanding	$ 0	£ 900,000	$ 9,000,000	$ 3,000,000	£ 0	$ 10,300,000

Derivative Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2024

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of Fair Value of Outstanding Derivative contracts

The fair value of the outstanding derivative contracts recorded in the balance sheet are as follows:


			March 31, 2024
	Copper Swap Contracts		Heating Oil Contracts		Foreign Currency Forward Contracts		Interest Rate Swap Contracts			Total
(Dollars in millions)
Derivative contracts	$	7.7	$	0.0	$	0.0	$	3.7		$	11.4
Other assets		1.1		0.0		0.0		1.3			2.4
Other long-term liabilities		0.0		0.0		0.0		(2.5	)		(2.5	)
Net asset on balance sheet	$	8.8	$	0.0	$	0.0	$	2.5		$	11.3
Accumulated other comprehensive gain, net of tax	$	4.5	$	0.0	$	0.0	$	1.8		$	6.3


			December 31, 2023
	Copper Swap Contracts		Heating Oil Contracts			Foreign Currency Forward Contracts			Interest Rate Swap Contracts			Total
(Dollars in millions)
Derivative contracts	$	4.1	$	0.0		$	0.2		$	2.8		$	7.1
Accrued liabilities		0.0		(0.3	)		(0.1	)		0.0			(0.4	)
Other long-term liabilities		0.0		0.0			0.0			(6.5	)		(6.5	)
Net asset (liability) on balance sheet	$	4.1	$	(0.3	)	$	0.1		$	(3.7	)	$	0.2
Accumulated other comprehensive gain (loss), net of tax	$	2.0	$	0.0		$	0.0		$	(2.9	)	$	(0.9	)

Schedule of Outstanding Copper Swap Contracts

As of the periods presented, we had outstanding copper swap contracts of the following amounts:


	Units Outstanding (in Pounds)				Net Fair Value – Asset
	March 31, 2024		December 31, 2023		March 31, 2024		December 31, 2023
(Amounts in millions)
Cash flow hedges		26.6		31.7	$	5.8	$	2.6
Contracts where hedge accounting was not elected		10.6		9.5		3.0		1.5
Total		37.2		41.2	$	8.8	$	4.1

Schedule of Unrealized Gain from Contract Where Hedge Accounting Was Not Elected

The unrealized gain from copper swaps contracts where hedge accounting was not elected is as follows:


	Three Months Ended March 31,
	2024		2023
(Dollars in millions)
Gain from contracts where hedge accounting was not elected	$	1.5	$	1.1

Summary of Net Currency Units Outstanding

The net currency units outstanding for contracts were:


	March 31, 2024		December 31, 2023
(In millions)
United States Dollars		USD 9.0		USD 10.3
British Pound Sterling		GBP 0.9		GBP 0.0
Australian Dollars		AUD 0.0		AUD 3.0

Condensed Consolidated Statement of Shareholders' Equity - USD ($)
$ in Millions

Total

Common Stock [Member]

Additional Paid-In Capital [Member]

Retained Earnings [Member]

Accumulated Other Comprehensive Loss [Member]

Treasury Stock [Member]

Noncontrolling Interests [Member]

Balance at Dec. 31, 2022

$ 403.0

$ 0.2

$ 263.9

$ 360.2

$ (97.3)

$ (127.6)

$ 3.6

Issuance of common stock

1.3

Employee stock plans

4.0

Net income attributable to Koppers

25.5

Common Stock dividends ($0.07 and $0.06 per share)

(1.5)

Currency translation adjustment

2.7

Cash flow hedges, net of tax

^[1]

4.7

Pension adjustments, net of tax

^[2]

0.3

Purchases

(5.8)

Net income attributable to noncontrolling interests

0.7

Balance at Mar. 31, 2023

434.9

269.2

384.2

(89.6)

(133.4)

4.3

Balance at Dec. 31, 2023

503.0

$ 0.3

291.1

444.0

(88.8)

(147.7)

4.1

Issuance of common stock

3.5

Employee stock plans

5.4

Net income attributable to Koppers

13.0

Common Stock dividends ($0.07 and $0.06 per share)

(1.6)

Currency translation adjustment

(13.9)

Cash flow hedges, net of tax

^[1]

7.0

Pension adjustments, net of tax

^[2]

0.4

Purchases

(6.9)

Net income attributable to noncontrolling interests

0.0

Balance at Mar. 31, 2024

$ 509.9

$ 300.0

$ 455.4

$ (95.3)

$ (154.6)

$ 4.1

[1]	Amounts reclassified from accumulated other comprehensive income to net income related to derivative financial instruments, net of tax, were $1.1 million and $1.7 million during the three months ended March 31, 2024 and 2023, respectively.
[2]	Amounts reclassified from accumulated other comprehensive income to net income consist of amounts shown for pension adjustments. This component of accumulated other comprehensive income is included in the computation of net periodic pension cost as disclosed in Note 10 – Pensions and Post-Retirement Benefit Plans.

Debt - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended
Debt - Additional Information (Detail) - USD ($)	Apr. 12, 2024	Apr. 30, 2023	Mar. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Revolving credit facility			$ 730,000,000
Long term debt			877,600,000	$ 849,400,000
Term Loan B [Member]
Debt Instrument [Line Items]
Debt instrument, payment terms		The principal balance of the Term Loan B is repayable in quarterly installments in an amount equal to 0.25 percent of the principal amount, commencing on January 1, 2024 and on the last business day of each quarterly period thereafter, with the balance due at maturity on April 10, 2030.
Long term debt			386,300,000	$ 388,000,000
Percentage of face value of issued debt		97.00%
Net proceeds from secured debt, before debt financing costs		$ 388,000,000
Debt instrument, basis spread on variable rate		3.50%
Debt instrument, floor interest rate		0.50%
Debt instrument, frequency of periodic payment		quarterly
Debt maturity date		Apr. 10, 2030
Debt instrument, percentage of principal payment		0.25%
Senior Secured Credit Facilities [Member]
Debt Instrument [Line Items]
Letters of credit, amount outstanding			7,800,000
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, notional value			$ 400,000,000
Fixed interest rate of loan portion			3.97%
Derivative, maturity date			Apr. 30, 2027
Revolving Credit Agreement [Member]
Debt Instrument [Line Items]
Revolving credit facility			$ 800,000,000
Swingline Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility			50,000,000
Credit Facility [Member] \| Senior Secured Credit Facilities [Member]
Debt Instrument [Line Items]
Debt instrument, unused borrowing capacity			$ 301,000,000
Subsequent Event [Member] \| Amendment No. 3 to Credit Facility [Member]
Debt Instrument [Line Items]
Secured term loan	$ 100,000,000
Debt instrument, floor interest rate	0.50%
Subsequent Event [Member] \| Amendment No. 3 to Credit Facility [Member] \| Term Loan B [Member]
Debt Instrument [Line Items]
Secured term loan	$ 497,000,000
Debt instrument, basis spread on variable rate	3.00%
Interest rate margin reduced	0.50%

Derivative Financial Instruments - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) Gallons	Dec. 31, 2023 Gallons
Derivative [Line Items]
Maximum period hedged in cash flow hedge	36 months
Number of derivative contract \| Gallons	1,700,000	1,500,000
Unrealized gains, reclassification period	12 months
Interest Rate Swaps [Member]
Derivative [Line Items]
Fixed interest rate of loan portion	3.97%
Derivative, notional value	$ 400.0
Derivative, maturity date	Apr. 30, 2027
Unrealized gains, net of tax, expected to be reclassified from other comprehensive income into earnings	$ 2.8
Commodity Price Hedging [Member]
Derivative [Line Items]
Unrealized gains, net of tax, expected to be reclassified from other comprehensive income into earnings	$ 4.2

Stock-based Compensation - Summary of Status and Activity of Stock Options (Detail) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) $ / shares shares
Share-Based Payment Arrangement [Abstract]
Options, Outstanding at December 31, 2023 \| shares	706,868
Option, Exercised \| shares	(132,131)
Options, Outstanding at March 31, 2024 \| shares	574,737
Options, Exercisable at March 31, 2024 \| shares	502,962
Weighted Average Exercise Price per Option, Outstanding at December 31, 2023 \| $ / shares	$ 27.51
Weighted Average Exercise Price per Option, Exercised \| $ / shares	26.78
Weighted Average Exercise Price per Option, Outstanding at March 31, 2024 \| $ / shares	27.67
Weighted Average Exercise Price per Option, Exercisable at March 31, 2024 \| $ / shares	$ 27.14
Weighted Average Remaining Contractual Term, Outstanding at March 31, 2024	4 years 10 months 2 days
Weighted Average Remaining Contractual Term, Exercisable at March 31, 2024	4 years 5 months 15 days
Aggregate Intrinsic Value, Outstanding at March 31, 2024 \| $	$ 15.8
Aggregate Intrinsic Value, Exercisable at March 31, 2024 \| $	$ 14.1

Income Taxes - Summary of Income Taxes Reconciled with Federal Statutory Rate (Detail)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Tax Disclosure [Abstract]
Federal income tax rate	21.00%	21.00%
Foreign earnings taxed at different rates	4.30%	4.30%
Nondeductible expenses	1.80%	1.40%
State income taxes, net of federal tax benefit	1.10%	1.30%
Change in tax contingency reserves	0.10%	0.00%
GILTI inclusion, net of foreign tax credits	0.00%	0.40%
Estimated annual effective income tax rate	28.30%	28.40%

Condensed Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Accounts receivable, allowance	$ 6.7	$ 6.5
Property, plant and equipment, accumulated depreciation	$ 479.4	$ 473.2
Senior Convertible Preferred Stock, par value	$ 0.01	$ 0.01
Senior Convertible Preferred Stock, shares authorized	10,000,000	10,000,000
Senior Convertible Preferred Stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	80,000,000	80,000,000
Common Stock, shares issued	25,630,272	25,163,238
Treasury stock, shares	4,441,930	4,302,996

Stock-based Compensation - Summary of Status and Activity of Non-Vested Stock Units (Detail)	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	1,112,102
Granted	327,823
Credited from dividends	170
Vested	(346,283)
Forfeited	(6,437)
Non-vested, Ending Balance	1,087,375
Beginning Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit \| $ / shares	$ 33.62
Granted, Weighted Average Grant Date Fair Value per Unit \| $ / shares	48.95
Credited from dividends, Weighted Average Grant Date Fair Value per Unit \| $ / shares	43
Vested, Weighted Average Grant Date Fair Value per Unit \| $ / shares	32.83
Forfeited, Weighted Average Grant Date Fair Value per Unit \| $ / shares	31.91
Ending Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit \| $ / shares	$ 38.5
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	531,339
Granted	145,627
Credited from dividends	170
Vested	(209,723)
Forfeited	(4,239)
Non-vested, Ending Balance	463,174
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	580,763
Granted	182,196
Credited from dividends	0
Vested	(136,560)
Forfeited	(2,198)
Non-vested, Ending Balance	624,201

Commitments and Contingent Liabilities

3 Months Ended

Mar. 31, 2024

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingent Liabilities

13. Commitments and Contingent Liabilities

We are involved in litigation and various proceedings relating to environmental laws and regulations, product liability and other matters. Certain of these matters are discussed below. The ultimate resolution of these contingencies is subject to significant uncertainty and should we fail to prevail in any of these legal matters or should several of these legal matters be resolved against us in the same reporting period, these legal matters could, individually or in the aggregate, be material to the condensed consolidated financial statements.

Legal Proceedings

Coal Tar Pitch Cases. Koppers Inc. is one of several defendants in lawsuits filed in two states in which the plaintiffs claim they suffered a variety of illnesses (including cancer) as a result of exposure to coal tar pitch sold by the defendants. There were 51 plaintiffs in 27 cases pending as of March 31, 2024 and December 31, 2023. As of March 31, 2024 and December 31, 2023, there were 26 cases pending in the Court of Common Pleas of Allegheny County, Pennsylvania, and one case pending in the Circuit Court of Knox County, Tennessee.

The plaintiffs in all 27 pending cases seek to recover compensatory damages. Plaintiffs in 24 of those cases also seek to recover punitive damages. The plaintiffs in the 26 cases filed in Pennsylvania seek unspecified damages in excess of the court’s minimum jurisdictional limit. The plaintiff in the Tennessee state court case seeks damages of $15.0 million. The other defendants in these lawsuits vary from case to case and include companies such as Beazer East, Inc. (Beazer East), Honeywell International Inc., Graftech International Holdings, UCAR Carbon Company, Inc., and SGL Carbon Corporation. Discovery is proceeding in these cases. No trial dates have been set in any of these cases.

We have not provided a reserve for the coal tar pitch lawsuits because, at this time, we cannot reasonably determine the probability of a loss, and the amount of loss, if any, cannot be reasonably estimated. The timing of resolution of these cases cannot be reasonably determined. Although Koppers Inc. is vigorously defending these cases, an unfavorable resolution of these matters may have a material adverse effect on our business, financial condition, cash flows and results of operations.

Environmental and Other Litigation Matters

We are subject to federal, state, local and foreign laws and regulations and potential liabilities relating to the protection of the environment and human health and safety including, among other things, the cleanup of contaminated sites, the treatment, storage and disposal of wastes, the discharge of effluent into waterways, the emission of substances into the air and various health and safety matters. We expect to incur substantial costs for ongoing compliance with such laws and regulations. We may also face governmental or third-party claims, or otherwise incur costs, relating to cleanup of, or for injuries resulting from, contamination at sites associated with past and present operations. We accrue for environmental liabilities when a determination can be made that a liability is probable and reasonably estimable.

Environmental and Other Liabilities Retained or Assumed by Others. We have agreements with former owners of certain of our operating locations under which the former owners retained, assumed and/or agreed to indemnify us against certain environmental and other liabilities. The most significant of these agreements was entered into at Koppers Inc.’s formation on December 29, 1988 (the Acquisition). Under the related asset purchase agreement between Koppers Inc. and Beazer East, subject to certain limitations, Beazer East retained the responsibility for and agreed to indemnify Koppers Inc. against certain liabilities, damages, losses and costs, including, with certain limited exceptions, liabilities under and costs to comply with environmental laws to the extent attributable to acts or omissions occurring prior to the Acquisition and liabilities related to products sold by Beazer East prior to the Acquisition (the Indemnity). Beazer Limited, the parent company of Beazer East, unconditionally guaranteed Beazer East’s performance of the Indemnity pursuant to a guarantee.

The Indemnity provides different mechanisms, subject to certain limitations, by which Beazer East is obligated to indemnify Koppers Inc. with regard to certain environmental, product and other liabilities and imposes certain conditions on Koppers Inc. before receiving such indemnification, including, in some cases, certain limitations regarding the time period as to which claims for indemnification can be brought. In July 2004, Koppers Inc. and Beazer East agreed to amend the environmental indemnification provisions of the December 29, 1988 asset purchase agreement to extend the indemnification period for pre-closing environmental liabilities, subject to the following paragraph, and agreed to share toxic tort litigation defense arising from any sites acquired from Beazer East.

Qualified expenditures under the Indemnity are not subject to a monetary limit. Qualified expenditures under the Indemnity include (i) environmental cleanup liabilities required by third parties, such as investigation, remediation and closure costs, relating to pre-December 29, 1988 (Pre-Closing) acts or omissions of Beazer East or its predecessors; (ii) environmental claims by third parties for personal injuries, property damages and natural resources damages relating to Pre-Closing acts or omissions of Beazer East or its predecessors; (iii) punitive damages for the acts or omissions of Beazer East and its predecessors without regard to the date of the alleged conduct and (iv) product liability claims for products sold by Beazer East or its predecessors without regard to the date of the alleged conduct. The indemnification period ended July 14, 2019 (the Claim Deadline) and Beazer East may now tender certain third-party claims described in sections (i) and (ii) above to Koppers Inc. However, to the extent the third-party claims described in sections (i) and (ii) above were tendered to Beazer East by the Claim Deadline, Beazer East will continue to be required to pay the costs arising from such claims under the Indemnity. Furthermore, the Claim Deadline did not change the provisions of the Indemnity with respect to indemnification for non-environmental claims, such as product liability claims, which claims may continue to be tendered by Koppers Inc. to Beazer East.

The Indemnity provides for the resolution of issues between Koppers Inc. and Beazer East by an arbitrator on an expedited basis upon the request of either party. The arbitrator could be asked, among other things, to make a determination regarding the allocation of environmental responsibilities between Koppers Inc. and Beazer East. Arbitration decisions under the Indemnity are final and binding on the parties.

Contamination has been identified at most manufacturing and other sites of our subsidiaries. One site currently owned and operated by Koppers Inc. in the United States is listed on the National Priorities List promulgated under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, as amended (CERCLA). Currently, at the properties acquired from Beazer East (which includes the National Priorities List site and all but one of the sites permitted under the Resource Conservation and Recovery Act (RCRA)), a significant portion of all investigative, cleanup and closure activities are being conducted and paid for by Beazer East pursuant to the terms of the Indemnity. In addition, other of Koppers Inc.’s sites are or have been operated under RCRA and various other environmental permits, and remedial and closure activities are being conducted at some of these sites.

To date, the parties that retained, assumed and/or agreed to indemnify us against the liabilities referred to above, including Beazer East, have performed their obligations in all material respects. Periodically, issues have arisen between Koppers Inc. and Beazer East and/or other indemnitors that have been resolved without arbitration. Koppers Inc. and Beazer East engage in discussions from time to time that involve, among other things, the allocation of environmental costs related to certain operating and closed facilities.

If for any reason (including disputed coverage or financial incapability) one or more of such parties fail to perform their obligations and we are held liable for or otherwise required to pay all or part of such liabilities without reimbursement, the imposition of such liabilities on us could have a material adverse effect on our business, financial condition, cash flows and results of operations. Furthermore, we could be required to record a contingent liability on our balance sheet with respect to such matters, which could result in a negative impact to our business, financial condition, cash flows and results of operations.

Domestic Environmental Matters. Koppers Inc. has been named as one of the potentially responsible parties (PRPs) at the Portland Harbor CERCLA site located on the Willamette River in Oregon. Koppers Inc. operated a coal tar pitch terminal near the site. Koppers Inc. has responded to an EPA information request and has executed a PRP agreement which outlines a private process to develop an allocation of past and future costs among more than 80 parties to the site. Koppers Inc. believes it is a de minimis contributor at the site.

The EPA issued its Record of Decision (ROD) in January 2017 for the Portland Harbor CERCLA site. The selected remedy includes a combination of sediment removal, capping, enhanced and monitored natural recovery and riverbank improvements. The ROD does not determine who is responsible for remediation costs. At that time, the net present value and undiscounted costs of the selected remedy as estimated in the ROD were approximately $1.1 billion and $1.7 billion, respectively. These costs are likely to increase given recent submissions to EPA regarding remedy design and because the remedy will not be implemented for several years. Responsibility for implementing and funding that work is yet to be determined. The funding of that work amongst the PRPs is the subject of a separate private allocation process which is ongoing.

Additionally, Koppers Inc. is involved in two separate matters involving natural resource damages at the Portland Harbor site. One matter involves claims by the trustees to recover damages based upon an assessment of damages to natural resources caused by the releases of hazardous substances to the Willamette River. The assessment serves as the foundation to estimate liabilities for settlements of natural resource damages claims or litigation to recover from those who do not settle with the trustee groups. Koppers Inc. has been engaged in a process to resolve its natural resource damage liabilities for the assessment area. A second matter involves a lawsuit filed in January 2017 by the Yakama Nation in Oregon federal court. Yakama Nation seeks recovery for response costs and the costs of assessing injury to natural resources in waterways beyond the current assessment area. Following the most recent court rulings, the Yakama Nation case has been stayed pending completion of the private allocation process for the Portland Harbor CERCLA site.

In September 2009, Koppers Inc. received a general notice letter stating that it may be a PRP at the Newark Bay CERCLA site. In January 2010, Koppers Inc. submitted a response to the general notice letter asserting that Koppers Inc. is a de minimis party at this site.

We have accrued the estimated costs of participating in the PRP group at the Portland Harbor and Newark Bay CERCLA sites and estimated de minimis contributor settlement amounts at the sites totaling $3.9 million as of March 31, 2024. The actual cost could be materially higher as there has not been a determination of how those costs will be allocated among the PRPs at the sites. Accordingly, an unfavorable resolution of these matters may have a material adverse effect on our business, financial condition, cash flows and results of operations.

There are two plant sites related to the Performance Chemicals business and one plant site related to the Utility and Industrial Products business in the United States where we have recorded environmental remediation liabilities for soil and groundwater contamination which occurred prior to our acquisition of the businesses. As of March 31, 2024, our estimated environmental remediation liability for these acquired sites totals $3.8 million.

Foreign Environmental Matters. There is one plant site related to the Performance Chemicals business located in Australia where we have recorded an environmental remediation liability for soil and groundwater contamination which occurred prior to the acquisition of the business. As of March 31, 2024, our estimated environmental remediation liability for the acquired site totals $1.2 million.

Environmental Reserves Rollforward. The following table reflects changes in the accrual for environmental remediation. A total of $2.2 million was classified as current liabilities as of March 31, 2024 and December 31, 2023.


	Period ended
	March 31, 2024			December 31, 2023
(Dollars in millions)
Balance at beginning of period	$	10.6		$	10.9
Expense		0.0			0.2
Cash expenditures		0.0			(0.4	)
Currency translation		(0.1	)		(0.1	)
Balance at end of period	$	10.5		$	10.6

Inventories, Net - Components of Net Inventories (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Inventory Disclosure [Abstract]
Raw materials	$ 348.4	$ 348.4
Work in process	15.8	17.9
Finished goods	147.0	139.0
Total	511.2	505.3
Less revaluation to LIFO	112.2	109.6
Net	$ 399.0	$ 395.7

Condensed Consolidated Balance Sheet - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Assets
Cash and cash equivalents	$ 49.0	$ 66.5
Accounts receivable, net of allowance of $6.7 and $6.5	218.3	202.4
Inventories, net	399.0	395.7
Derivative contracts	11.4	7.1
Other current assets	30.0	27.3
Total current assets	707.7	699.0
Property, plant and equipment, net of accumulated depreciation of $479.4 and $473.2	640.5	631.7
Goodwill	293.1	294.4
Intangible assets, net	98.5	102.2
Operating lease right-of-use assets	85.8	90.5
Deferred tax assets	9.8	10.4
Other assets	9.9	7.3
Total assets	1,845.3	1,835.5
Liabilities
Accounts payable	195.2	202.9
Accrued liabilities	87.5	95.1
Current operating lease liabilities	22.2	22.9
Current maturities of long-term debt	4.0	5.0
Total current liabilities	308.9	325.9
Long-term debt	865.1	835.4
Operating lease liabilities	63.4	67.4
Accrued postretirement benefits	27.9	31.6
Deferred tax liabilities	28.1	25.9
Other long-term liabilities	42.0	46.3
Total liabilities	1,335.4	1,332.5
Commitments and contingent liabilities (Note 13)
Equity
Senior Convertible Preferred Stock, $0.01 par value per share; 10,000,000 shares authorized; no shares issued	0.0	0.0
Common Stock, $0.01 par value per share; 80,000,000 shares authorized; 25,630,272 and 25,163,238 shares issued	0.3	0.3
Additional paid-in capital	300.0	291.1
Retained earnings	455.4	444.0
Accumulated other comprehensive loss	(95.3)	(88.8)
Treasury stock, at cost, 4,441,930 and 4,302,996 shares	(154.6)	(147.7)
Total Koppers shareholders’ equity	505.8	498.9
Noncontrolling interests	4.1	4.1
Total equity	509.9	503.0
Total liabilities and equity	$ 1,845.3	$ 1,835.5

Common Stock - Schedule of Changes in Common Stock and Treasury Stock (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Equity [Abstract]
Common Stock, balance at beginning of period	25,163,238	24,547,000
Common Stock, issued for employee stock plans	467,000	238,000
Common Stock, balance at end of period	25,630,272	24,785,000
Treasury Stock, balance at beginning of period	(4,302,996)	(3,784,000)
Treasury Stock, shares repurchased	(139,000)	(178,000)
Treasury Stock, balance at end of period	(4,441,930)	(3,962,000)
Common Stock Outstanding	21,188,000	20,823,000

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Mar. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Earnings and Dividends per Common Share

3 Months Ended

Mar. 31, 2024

Earnings Per Share [Abstract]

Earnings and Dividends per Common Share

5. Earnings and Dividends per Common Share

The following table sets forth the computation of basic and diluted earnings per common share:


	Three Months Ended March 31,
	2024		2023
(Dollars in millions, except share and per share amounts)
Net income attributable to Koppers	$	13.0	$	25.5
Weighted average common shares outstanding (in thousands):
Basic		21,066		20,842
Effect of dilutive securities		843		543
Diluted		21,909		21,385
Earnings per common share:
Basic	$	0.61	$	1.22
Diluted		0.59		1.19
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share		55		629

On May 2, 2024, we declared a quarterly dividend of $0.07 per common share, payable on June 10, 2024 to shareholders of record as of May 24, 2024.

Earnings and Dividends per Common Share - Schedule of Computation of Basic and Diluted Earnings per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share [Abstract]
Net income attributable to Koppers	$ 13.0	$ 25.5
Weighted average common shares outstanding (in thousands):
Basic	21,066	20,842
Effect of dilutive securities	843	543
Diluted	21,909	21,385
Earnings per common share – continuing operations:
Basic	$ 0.61	$ 1.22
Diluted	$ 0.59	$ 1.19
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share	55	629

Earnings and Dividends per Common Share - Additional Information (Detail) - $ / shares		3 Months Ended
	May 02, 2024	Mar. 31, 2024	Mar. 31, 2023
Dividends Payable [Line Items]
Quarterly dividend declared per common share		$ 0.07	$ 0.06
Subsequent Event [Member]
Dividends Payable [Line Items]
Quarterly dividend, declared date	May 02, 2024
Quarterly dividend declared per common share	$ 0.07
Quarterly dividend, payable date	Jun. 10, 2024
Quarterly dividend, payable date of record	May 24, 2024

Segment Information - Summary of Assets and Goodwill by Segments (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Segment Reporting Asset Reconciling Item [Line Items]
Assets	$ 1,845.3	$ 1,835.5
Goodwill	293.1	294.4
Railroad and Utility Products and Services [Member] \| Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	759.3	743.7
Goodwill	120.5	120.6
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	530.9	520.6
Goodwill	172.6	173.8
Carbon Materials and Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	516.4	538.9
All Other [Member] \| Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	$ 38.7	$ 32.3

- Definition

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

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+ Details

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References + Details

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Schedule of Company's Financial Instruments

The following table presents the estimated fair values and the related carrying amounts of our financial instruments:


	March 31, 2024				December 31, 2023
	Fair Value		Carrying Value		Fair Value		Carrying Value
(Dollars in millions)
Financial assets:
Investments and other assets	$	1.3	$	1.3	$	1.3	$	1.3
Financial liabilities:
Long-term debt (including current portion)	$	888.3	$	877.6	$	860.4	$	849.4

Stock-based Compensation - Schedule of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Stock-based compensation expense recognized:
Less related income tax benefit	$ 1.5	$ 1.1
Decrease in net income attributable to Koppers	3.9	2.9
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense recognized:
Stock-based compensation expense	$ 5.4	$ 4.0

Pensions and Post-Retirement Benefit Plans

3 Months Ended

Mar. 31, 2024

Retirement Benefits [Abstract]

Pensions and Post-Retirement Benefit Plans

10. Pensions and Post-Retirement Benefit Plans

We maintain a number of defined benefit and defined contribution plans to provide retirement benefits for employees in the United States, as well as employees outside the United States.

We are evaluating the termination of our United States qualified pension plan and are targeting the potential completion of this effort in the first quarter 2025. We estimate that a termination will require additional cash funding of $25 million and will result in an estimated settlement loss of $40 million, before tax, subject to changes to certain assumptions including the discount rate.

In connection with the planned termination of our defined benefit pension plan in the United Kingdom, in 2021, we entered into a buy-in bulk annuity insurance policy in exchange for a premium payment of $67.8 million, which is subject to adjustment as a result of subsequent data cleansing activities. Under the terms of this buy-in insurance policy, the insurer is liable to pay the benefits of the plan, but the plan still retains full legal responsibility to pay the benefits to members using the insurance payments. The buy-in policy will be treated as a plan asset going forward until such time as the buy-in policy is converted to a buy-out policy, which is when individual insurance policies will be assigned to each member of the plan and the plan will no longer have legal responsibility to pay the benefits to the members. The data cleansing effort has been substantially completed and we expect to recognize a pre-tax pension settlement loss of approximately $20 million upon the pension obligation becoming irrevocably settled.

The timing of the conversion to a buy-out policy may be impacted by a ruling from the High Court of Justice in the United Kingdom in the case of Virgin Media Limited v NTL Pension Trustees II Limited and Others related to certain amendments to UK pension plans. This ruling is currently under appeal.

The following table provides the components of net periodic benefit cost for the pension plans:


	Three Months Ended March 31,
	2024			2023
(Dollars in millions)
Service cost	$	0.4		$	0.4
Interest cost		1.9			2.1
Expected return on plan assets		(1.5	)		(1.7	)
Amortization of net loss		0.5			0.5
Net periodic benefit cost	$	1.3		$	1.3
Defined contribution plan expense	$	3.0		$	2.5

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480794/715-70-50-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (q)
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Subparagraph (l)
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//715/tableOfContent

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iii)
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-Name Accounting Standards Codification
-Section 50
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-Subparagraph (o)
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480126/715-20-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 60
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480266/715-60-50-3

+ Details

Comprehensive Income (Loss) and Equity - Schedule of Changes in Equity (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	$ 503.0		$ 403.0
Net income (loss)	13.0	$ 26.2	26.2
Other comprehensive (loss) income
Unrealized gain (loss) on cash flow hedges	7.0		4.7
Balance	509.9		434.9
Common Stock [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	0.3		0.2
Additional Paid-In Capital [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	291.1		263.9
Issuance of common stock	3.5		1.3
Other comprehensive (loss) income
Balance	300.0		269.2
Retained Earnings [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	444.0		360.2
Common Stock dividends ($0.07 and $0.06 per share)	(1.6)		(1.5)
Other comprehensive (loss) income
Balance	455.4		384.2
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(88.8)		(97.3)
Other comprehensive (loss) income
Balance	(95.3)		(89.6)
Treasury Stock [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(147.7)		(127.6)
Repurchases of common stock	(6.9)		(5.8)
Other comprehensive (loss) income
Balance	(154.6)		(133.4)
Noncontrolling Interests [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	4.1		3.6
Other comprehensive (loss) income
Balance	$ 4.1		$ 4.3

Stock-based Compensation

3 Months Ended

Mar. 31, 2024

Share-Based Payment Arrangement [Abstract]

Stock-based Compensation

6. Stock-based Compensation

The board of directors granted restricted stock units and performance stock units (collectively, the stock units) to certain employee participants in January 2024. No stock options were granted in 2024. Starting in 2023, most grants of restricted stock units vest in three years. Performance stock units have vesting based upon either a performance condition or a market condition. Performance stock units granted with a performance condition have a cumulative three-year performance objective based on adjusted EBITDA (see Note 7 – Segment Information). For performance stock units granted with a market condition, the applicable objective is based on our total shareholder return relative to the Standard & Poor’s SmallCap 600 Materials Index and has multi-year performance objectives. Both types of performance stock units have a three-year period for vesting, if the applicable performance objectives are achieved.

The number of performance stock units granted represents the target award and participants have the ability to earn between zero and 200 percent of the target award based upon actual performance. If minimum performance criteria are not achieved, no performance stock units will vest. For the awards granted in January 2024, target shares for units with a market condition totaled 56,796 and target shares for units with a performance condition totaled 125,399.

We calculated the fair value of the restricted stock units and performance stock units with a performance condition using the market price of the underlying common stock on the date of grant. We calculated the fair value of the performance stock units with a market condition on the date of grant using a Monte Carlo valuation model and the assumptions listed below:


	January 2024 Grant
Grant date price per share of performance award	$	46.68
Expected volatility		38.14	%
Risk-free interest rate		4.14	%
Look-back period in years		3.00
Grant date fair value per share	$	59.41

The following table shows a summary of the status and activity of non-vested stock units:


	Restricted Stock Units			Performance Stock Units			Total Stock Units			Weighted Average Grant Date Fair Value per Unit
Non-vested at December 31, 2023		531,339			580,763			1,112,102		$	33.62
Granted		145,627			182,196			327,823		$	48.95
Credited from dividends		170			0			170		$	43.00
Vested		(209,723	)		(136,560	)		(346,283	)	$	32.83
Forfeited		(4,239	)		(2,198	)		(6,437	)	$	31.91
Non-vested at March 31, 2024		463,174			624,201			1,087,375		$	38.50

The following table shows a summary of the status and activity of stock options:


	Options			Weighted Average Exercise Price per Option		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2023		706,868		$	27.51
Exercised		(132,131	)	$	26.78
Outstanding at March 31, 2024		574,737		$	27.67		4.84	$	15.8
Exercisable at March 31, 2024		502,962		$	27.14		4.46	$	14.1

The following table presents total stock-based compensation expense recognized in the condensed consolidated statement of operations:


	Three Months Ended March 31,
	2024		2023
(Dollars in millions)
Selling, general and administrative expenses	$	5.4	$	4.0
Less related income tax benefit		1.5		1.1
Decrease in net income attributable to Koppers	$	3.9	$	2.9

Pensions and Post-Retirement Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2024

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost for Pension Plans

The following table provides the components of net periodic benefit cost for the pension plans:


	Three Months Ended March 31,
	2024			2023
(Dollars in millions)
Service cost	$	0.4		$	0.4
Interest cost		1.9			2.1
Expected return on plan assets		(1.5	)		(1.7	)
Amortization of net loss		0.5			0.5
Net periodic benefit cost	$	1.3		$	1.3
Defined contribution plan expense	$	3.0		$	2.5

New Accounting Pronouncements	3 Months Ended
New Accounting Pronouncements	Mar. 31, 2024
Accounting Changes and Error Corrections [Abstract]
New Accounting Pronouncements	2. New Accounting Pronouncements In November 2023, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. This ASU updates reportable segment disclosures by expanding the frequency and extent of segment disclosures. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023, and for interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. The amendments should be applied retrospectively to all prior periods presented in the financial statements. We are currently evaluating this ASU to determine its impact on our disclosures. In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. This ASU updates income tax disclosures by requiring annual disclosures of consistent categories and greater disaggregation of information in the rate reconciliation and income taxes paid disaggregated by jurisdiction. ASU No. 2023-09 is effective for fiscal years beginning after December 15, 2024. Early adoption is permitted. The amendments should be applied on a prospective basis. We are currently evaluating this ASU to determine its impact on our disclosures.

- Definition

The entire disclosure for change in accounting principle. Includes, but is not limited to, nature, reason, and method of adopting amendment to accounting standards or other change in accounting principle.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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-Name Accounting Standards Codification
-Section 65
-Paragraph 2
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2024	Apr. 30, 2024
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Trading Symbol	KOP
Entity Registrant Name	KOPPERS HOLDINGS INC.
Entity Central Index Key	0001315257
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		21,200,184
Title of 12(b) Security	Common Stock
Security Exchange Name	NYSE
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity File Number	1-32737
Entity Tax Identification Number	20-1878963
Entity Address, Address Line One	436 Seventh Avenue
Entity Address, City or Town	Pittsburgh
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	15219
City Area Code	412
Local Phone Number	227-2001
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	PA

Segment Information - Summary of Results of Segment Operations (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023
Revenues from external customers:
Depreciation and amortization expense	$ 16.1		$ 14.0
Items excluded from the determination of segment profit:
LIFO expense	(2.6)		(0.3)
Gain on sale of assets	0.0		1.8
Mark-to-market commodity hedging gains	1.7		1.1
Interest expense	(17.1)		(14.0)
Depreciation and amortization	(16.1)		(14.0)
Income tax provision	(4.4)		(9.9)
Net income	13.0	$ 26.2	26.2
Operating Segments [Member] \| Railroad and Utility Products and Services [Member]
Revenues from external customers:
Depreciation and amortization expense	6.9		5.9
Adjusted EBITDA:
Adjusted EBITDA	17.7		15.8
Operating Segments [Member] \| Performance Chemicals [Member]
Revenues from external customers:
Depreciation and amortization expense	3.4		3.5
Adjusted EBITDA:
Adjusted EBITDA	29.8		26.3
Operating Segments [Member] \| Carbon Materials and Chemicals [Member]
Revenues from external customers:
Depreciation and amortization expense	4.0		19.4
Adjusted EBITDA:
Adjusted EBITDA	$ 5.8		$ 4.6

Pensions and Post-Retirement Benefit Plans - Components of Net Periodic Benefit Cost for Pension Plans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Postemployment Benefits [Abstract]
Service cost	$ 0.4	$ 0.4
Interest cost	1.9	2.1
Expected return on plan assets	(1.5)	(1.7)
Amortization of net loss	0.5	0.5
Net periodic benefit cost	1.3	1.3
Defined contribution plan expense	$ 3.0	$ 2.5

Derivative Financial Instruments - Schedule of Unrealized Gain from Contract Where Hedge Accounting Was Not Elected (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Hedges [Member] \| Contracts Where Hedge Accounting Was not Elected [Member]
Derivative [Line Items]
Gain from contracts where hedge accounting was not elected	$ 1.5	$ 1.1