Koppers (KOP) 10-K 27 Feb 23 2022 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Jan. 31, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Trading Symbol	KOP
Entity Registrant Name	KOPPERS HOLDINGS INC.
Entity Central Index Key	0001315257
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		20,830,370
Entity Public Float			$ 458.5
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock
Security Exchange Name	NYSE
Entity File Number	1-32737
Entity Incorporation, State or Country Code	PA
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 Annual Report	true
Document Transition Report	false
ICFR Auditor Attestation Flag	true
Documents Incorporated by Reference	Portions of the registrant’s definitive Proxy Statement for the 2023 Annual Meeting of Shareholders are incorporated by reference into Part III of this Annual Report on Form 10-K.
Auditor Name	KPMG LLP
Auditor Location	Pittsburgh, Pennsylvania (US Firm)
Auditor Firm ID	185

Consolidated Statement of Opera

Consolidated Statement of Operations - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Net sales	$ 1,980.5	$ 1,678.6	$ 1,669.1
Cost of sales	1,635.9	1,344.5	1,308.7
Depreciation and amortization	56.1	57.7	54.1
Selling, general and administrative expenses	153.3	148.9	143.1
Impairment and restructuring charges	0	2.2	6.5
(Gain) on sale of assets	(2.5)	(31.2)	0
Operating profit	137.7	156.5	156.7
Other income, net	2.5	3.6	2.3
Interest expense	44.8	40.5	48.9
Income from continuing operations before income taxes	95.4	119.6	110.1
Income tax provision	31.6	34.5	21
Income from continuing operations	63.8	85.1	89.1
(Loss) gain on sale of discontinued operations, net of tax benefit (expense) of $0.0, $0.1 and $(7.4)	(0.6)	(0.2)	31.9
Net income	63.2	84.9	121
Net (loss) attributable to noncontrolling interests	(0.2)	(0.3)	(1)
Net income attributable to Koppers	$ 63.4	$ 85.2	$ 122
Basic -
Continuing operations	$ 3.05	$ 4.02	$ 4.25
Discontinued operations	(0.03)	(0.02)	1.56
Earnings per basic common share	3.02	4	5.81
Diluted -
Continuing operations	3	3.90	4.17
Discontinued operations	(0.02)	(0.02)	1.54
Earnings per diluted common share	$ 2.98	$ 3.88	$ 5.71
Weighted average shares outstanding (in thousands):
Basic	20,977	21,238	20,992
Diluted	21,313	21,925	21,374

Consolidated Statement of Ope_2

Consolidated Statement of Operations (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Income (loss) from discontinued operations, tax benefit (expense)	$ 0	$ 0.1	$ (7.4)

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 63.2	$ 84.9	$ 121
Changes in other comprehensive (loss) income:
Currency translation adjustment	(21.6)	(16.4)	22.8
Unrealized (loss) gain on cash flow hedges, net of tax benefit (expense) of $6.3, $0.5 and $(12.6)	(38.8)	(3.8)	41.2
Unrecognized pension prior service cost, net of tax benefit of $0.0, $0.0 and $0.0	0	0.1	0
Unrecognized pension net gain (loss), net of tax benefit (expense) of $(0.5), $1.3 and $0.4	2.7	(3.8)	(1.1)
Total comprehensive income	5.5	61	183.9
Comprehensive (loss) income attributable to noncontrolling interests	(0.5)	(0.2)	0.1
Comprehensive income attributable to Koppers	$ 6	$ 61.2	$ 183.8

Consolidated Statement of Com_2

Consolidated Statement of Comprehensive (Loss) Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Tax benefit (expense), unrealized gains on cash flow hedges	$ 6.1	$ 0.5	$ (12.6)
Unrecognized pension prior service cost, tax benefit	0	0	0
Tax benefit (expense), unrecognized pension net income	$ (0.5)	$ 1.3	$ 0.4

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Assets
Cash and cash equivalents	$ 33.3	$ 45.5
Accounts receivable, net of allowance of $3.5 and $3.3	215.7	182.8
Inventories, net	355.7	313.8
Derivative contracts	3.1	61
Other current assets	29	25
Total current assets	636.8	628.1
Property, plant and equipment, net	557.3	489.1
Operating lease right-of-use assets	86.3	91.2
Goodwill	294	296
Intangible assets, net	116.1	131.5
Deferred tax assets	11.7	15
Other assets	9.2	11
Total assets	1,711.4	1,661.9
Liabilities
Accounts payable	207.4	171.9
Accrued liabilities	96.1	90.5
Current operating lease liabilities	20.5	21.3
Current maturities of long-term debt	0	2
Total current liabilities	324	285.7
Long-term debt	817.7	781.5
Accrued postretirement benefits	34.7	38.6
Deferred tax liabilities	21.5	33.4
Operating lease liabilities	66.3	70.3
Other long-term liabilities	44.2	41.6
Total liabilities	1,308.4	1,251.1
Commitments and contingent liabilities (Note 19)
Equity
Senior Convertible Preferred Stock, $0.01 par value per share; 10,000,000 shares authorized; no shares issued	0	0
Common Stock, $0.01 par value per share; 80,000,000 shares authorized; 24,547,000 and 24,026,844 shares issued	0.2	0.2
Additional paid-in capital	263.9	249.5
Retained earnings	360.2	300.9
Accumulated other comprehensive loss	(97.3)	(40)
Treasury stock, at cost, 3,783,901 and 2,930,694 shares	(127.6)	(104)
Total Koppers shareholders’ equity	399.4	406.6
Noncontrolling interests	3.6	4.2
Total equity	403	410.8
Total liabilities and equity	$ 1,711.4	$ 1,661.9

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Accounts receivable, allowance	$ 3.5	$ 3.3
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	24,547,000	24,026,844
Treasury stock, shares	3,783,901	2,930,694

Consolidated Statement of Cash

Consolidated Statement of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash provided by (used in) operating activities:
Net income	$ 63.2	$ 84.9	$ 121
Adjustments to reconcile net cash provided by (used in) operating activities:
Depreciation and amortization	56.1	57.7	54.1
Stock-based compensation	13.2	13	11.3
Change in derivative contracts	6.5	3.8	(9.2)
Non-cash interest expense	2.8	2.7	2.6
Loss (gain) on sale of discontinued operations	0	0.3	(35.8)
(Gain) on sale of assets and investment	(2.6)	(31.5)	0
Insurance proceeds	(0.8)	(6.1)	(0.7)
Deferred income taxes	2.7	16.9	9.4
Change in other liabilities	1.1	2.1	(8.6)
Other - net	5.3	4	(0.4)
Changes in working capital:
Accounts receivable	(32.3)	(12.7)	(11.5)
Inventories	(41.8)	(24.3)	8.7
Accounts payable	32.7	20.9	(25.3)
Accrued liabilities	(7.3)	(21)	8.5
Other working capital	3.5	(7.7)	3
Net cash provided by operating activities	102.3	103	127.1
Cash (used in) provided by investing activities:
Capital expenditures	(105.3)	(125)	(69.8)
Insurance proceeds	0.8	6.1	0.7
Acquisitions	(14.7)	0	0
Net cash provided by sale of discontinued operations and asset sales	4.4	29.4	74.7
Net cash (used in) provided by investing activities	(114.8)	(89.5)	5.6
Cash provided by (used in) financing activities:
Net increase (decrease) in credit facility borrowings	38.3	15.2	(57.3)
Repayments of long-term debt	(2)	(10.1)	(70.7)
Issuances of Common Stock	1.1	2.4	1.1
Repurchases of Common Stock	(23.6)	(11.5)	(1.6)
Payment of debt issuance costs	(4.8)	0	(0.2)
Dividends paid	(4.2)	0	0
Net cash provided by (used in) financing activities	4.8	(4)	(128.7)
Effect of exchange rate changes on cash	(4.5)	(2.5)	1.5
Change in cash and cash equivalents of discontinued operations held for sale	0	0	0.7
Net (decrease) increase in cash and cash equivalents	(12.2)	7	6.2
Cash and cash equivalents at beginning of period	45.5	38.5	32.3
Cash and cash equivalents at end of period	33.3	45.5	38.5
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash outflow from operating leases	29.3	30.5	31.5
Supplemental disclosure of non-cash investing and financing activities:
Right-of-use assets obtained in exchange for new operating lease liabilities	12.1	12.6	8.6
Cash paid during the year for:
Interest	41.3	38.1	50.1
Income taxes	20.7	23.4	13.4
Noncash investing activities:
Accrued capital expenditures	$ 11.1	$ 7.3	$ 8.9

Consolidated Statement of Share

Consolidated Statement of Shareholders' Equity - USD ($) $ in Millions	Total	Preferred Stock [Member] Senior Convertible Preferred Stock [Member]	Common Stock [Member]	Noncontrolling Interests [Member]	Retained Earnings (Accumulated Deficit) [Member]	Currency Translation Adjustment [Member]	Unrecognized Gains (Losses) on Cash Flow Hedges [Member]	Unrecognized Pension Prior Service Cost [Member]	Unrecognized Pension Net Loss [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Koppers Shareholder's Equity (Deficit) [Member]
Balance at Dec. 31, 2019		$ 0	$ 0.2	$ 11.4	$ 93.8	$ (39.8)	$ 3.2	$ (0.6)	$ (40.5)	$ 221.9	$ (90.9)
Net loss attributable to noncontrolling interests	$ (1)			(1)
Net income (loss) attributable to Koppers	122				122
Common Stock dividends					0
Purchases											(1.6)
Loss on sale of subsidiary						0
Change in currency translation adjustment	22.8			1.1		21.7
Reclassification of unrealized (gains) losses on cash flow hedges to expense, net of tax benefit (expense) of $(6.7), $7.2 and $0.1							(0.2)
Change in cash flow hedges, net of tax (expense) benefit of $12.8, $(6.7) and $(12.7)							41.4
Revaluation of unrecognized prior service benefit,net of tax benefit of $0.0, $0.0 and $0.0								0
Reclassification of unrecognized pension net loss to expense, net of tax expense of $0.4, $0.3 and $0.3									1.1
Revaluation of unrecognized pension net loss, net of tax(benefit) expense of $0.1, $(1.6) and $(0.7)									(2.2)
Sale of discontinued operations				(7.2)
Employee stock plans										11.3
Issuance of common stock										0.9
Balance at Dec. 31, 2020	346	0	0.2	4.3	215.8	(18.1)	44.4	(0.6)	(41.6)	234.1	(92.5)	$ (15.9)	$ 341.7
Net loss attributable to noncontrolling interests	(0.3)			(0.3)
Net income (loss) attributable to Koppers	85.2				85.2
Common Stock dividends					0
Purchases											(11.6)
Loss on sale of subsidiary						(4.4)
Change in currency translation adjustment	(16.4)			0.2		(12.2)
Reclassification of unrealized (gains) losses on cash flow hedges to expense, net of tax benefit (expense) of $(6.7), $7.2 and $0.1							(22.8)
Change in cash flow hedges, net of tax (expense) benefit of $12.8, $(6.7) and $(12.7)							19
Revaluation of unrecognized prior service benefit,net of tax benefit of $0.0, $0.0 and $0.0								0.1
Reclassification of unrecognized pension net loss to expense, net of tax expense of $0.4, $0.3 and $0.3									1.1
Revaluation of unrecognized pension net loss, net of tax(benefit) expense of $0.1, $(1.6) and $(0.7)									(4.9)
Sale of discontinued operations				0
Employee stock plans										13
Issuance of common stock										2.4
Balance at Dec. 31, 2021	410.8	$ 0	$ 0.2	4.2	301	(34.7)	40.6	(0.5)	(45.4)	249.5	(104.1)	(40)	406.6
Net loss attributable to noncontrolling interests	(0.2)			(0.2)
Net income (loss) attributable to Koppers	63.4				63.4
Common Stock dividends					(4.2)
Purchases											(23.5)
Loss on sale of subsidiary						0
Change in currency translation adjustment	(21.6)			(0.4)		(21.2)
Reclassification of unrealized (gains) losses on cash flow hedges to expense, net of tax benefit (expense) of $(6.7), $7.2 and $0.1							(40.4)
Change in cash flow hedges, net of tax (expense) benefit of $12.8, $(6.7) and $(12.7)							1.6
Revaluation of unrecognized prior service benefit,net of tax benefit of $0.0, $0.0 and $0.0								0
Reclassification of unrecognized pension net loss to expense, net of tax expense of $0.4, $0.3 and $0.3									1.3
Revaluation of unrecognized pension net loss, net of tax(benefit) expense of $0.1, $(1.6) and $(0.7)									1.4
Sale of discontinued operations				0
Employee stock plans										13.2
Issuance of common stock										1.2
Balance at Dec. 31, 2022	$ 403			$ 3.6	$ 360.2	$ (55.9)	$ 1.8	$ (0.5)	$ (42.7)	$ 263.9	$ (127.6)	$ (97.3)	$ 399.4

Consolidated Statement of Sha_2

Consolidated Statement of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Unrealized (gains) losses on cash flow hedges to expense, tax benefit (expense)	$ (6.1)	$ (0.5)	$ 12.6
Revaluation of unrecognized pension net loss, tax benefit	(0.1)	(1.6)	0.7
Unrecognized Gains (Losses) on Cash Flow Hedges [Member]
Unrealized (gains) losses on cash flow hedges to expense, tax benefit (expense)	6.7	7.2	(0.1)
Deferred losses on cash flow hedges, tax benefit (expense)	(12.8)	(6.7)	(12.7)
Unrecognized Pension Prior Service Cost [Member]
Revaluation of unrecognized prior service benefit, tax benefit	0	0	0
Unrecognized Pension Net Loss [Member]
Reclassification of unrecognized pension net loss, tax expense	$ 0.4	$ 0.3	$ 0.3

Description of Business

Description of Business	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Description of Business	1. Description of Business Parent company of Koppers Inc. – In these financial statements, unless otherwise indicated or the context requires otherwise, when the terms “Koppers,” the “Company,” “we,” “our” or “us,” are used, they mean Koppers Holdings Inc. (“Koppers Holdings”) and its subsidiaries on a consolidated basis. The use of these terms is not intended to imply that Koppers Holdings and Koppers Inc. are not separate and distinct legal entities from each other and from their respective subsidiaries. Koppers Holdings has no direct operations and no significant assets other than the stock of Koppers Inc. It depends on the dividends from the earnings of Koppers Inc. and its subsidiaries to generate the funds necessary to meet its financial obligations. The terms of Koppers Inc.’s Credit Facility (as defined in Note 15 - "Debt") prohibit Koppers Inc. from paying dividends and otherwise transferring assets except for certain limited dividends. Further, the terms of the indenture governing Koppers Inc.’s Senior Notes due 2025 significantly restrict Koppers Inc. from paying dividends and otherwise transferring assets to Koppers Holdings. Business description – We are a global integrated provider of treated wood products, wood treatment chemicals and carbon compounds for use in a variety of markets including the railroad, specialty chemical, utility, residential lumber, agriculture, aluminum, steel, rubber and construction industries. Our business is operated through three business segments, Railroad and Utility Products and Services (“RUPS”), Performance Chemicals (“PC”) and Carbon Materials and Chemicals (“CMC”). Our RUPS segment sells treated and untreated wood products, rail joint bars and services primarily to the railroad industry and treated wood products to the utility industry. Railroad products include procuring and treating items such as crossties, switch ties and various types of lumber used for railroad bridges and crossings and the manufacture of rail joint bars. Utility products include transmission and distribution poles and pilings. The segment also operates a railroad services business that conducts engineering, design, repair and inspection services for railroad bridges, a business related to the recovery of used crossties and utility poles and a business related to the inspection of utility poles. Our PC segment develops, manufactures, and markets wood preservation chemicals and wood treatment technologies and services a diverse range of end-markets including infrastructure, residential 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 which is used in the production of carbon black. Carbon pitch is a critical raw material used in the production of aluminum and for the production of steel in electric arc furnaces. 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.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of presentation – The consolidated financial statements include our accounts and all majority-owned subsidiaries for which we are deemed to exercise control over its operations. All significant intercompany transactions have been eliminated in consolidation. Certain prior period amounts in the Notes to Consolidated Financial Statements have been reclassified to conform to the current period’s presentation. Use of estimates – Accounting principles generally accepted in the United States require management to make estimates and judgments that affect the reported amounts of assets and liabilities and the disclosure of contingencies on the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Estimates have been prepared on the basis of the most current and best available information and actual results could differ materially from these estimates. Revenue recognition – Revenue is recognized upon the completion of performance obligations under our contracts with customers and when control of a good or service is transferred to the customer. Substantially all of our contracts with customers are ship and invoice arrangements where revenue is recognized when we complete our performance obligations and transfer control to the customer. Revenue recognition generally occurs at the point of shipment; however in certain circumstances as shipping terms dictate, we transfer control and revenue is recognized at the point of destination. Payment terms are typically within 45 days. Shipping and handling costs are included as a component of cost of sales. We recognize revenue related to the procurement of certain untreated railroad crossties upon delivery to our plant and acceptance by the customer. Service revenue, consisting primarily of wood treating services, is recognized at the time the service is provided and the performance obligation is satisfied. Payment on sales of untreated railroad crossties and wood treating services are generally due within 30 days of the invoice date. 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 consolidated balance sheet. Contract assets of $ 8.3 million and $ 7.9 million are recorded within accounts receivable, net of allowance within the consolidated balance sheet as of December 31, 2022 and December 31, 2021 , respectively. Cash and cash equivalents - Cash and cash equivalents include cash on hand and on deposit and investments with an original maturity of 90 days or less. Accounts receivable – We maintain allowances for doubtful accounts for estimated losses resulting from the inability of customers to make required payments. In circumstances where we become aware of a specific customer’s inability to meet its financial obligations to Koppers, a specific reserve for bad debts is recorded against amounts due. If the financial condition of our customers were to deteriorate, resulting in an inability to make payments, additional allowances may be required. Inventories – In the United States, CMC and RUPS inventories are valued at the lower of cost, utilizing the last-in, first-out (“LIFO”) basis, or net realizable value. Utilities and industrial products inventories are valued at the lower of cost, utilizing the moving average cost basis, or net realizable value. PC inventories and all other inventories outside of the United States are valued at the lower of cost, utilizing the first-in, first-out (“FIFO”) basis, and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. LIFO inventories constituted approximately 52 percent and 45 percent of the FIFO inventory value at December 31, 2022 and 2021, respectively. In 2022, 2021 and 2020 , we recorded inventory write-downs of $ 1.2 million, $ 0.6 million and $0 .6 million, respectively, related to lower of cost and net realizable value for our subsidiaries that value inventory on the FIFO basis. Property, plant and equipment – Property, plant and equipment are recorded at purchased cost and include improvements which significantly increase capacities or extend useful lives of existing plant and equipment. Depreciation expense is calculated by applying the straight-line method over estimated useful lives. Estimated useful lives for buildings generally range from ten to 20 years and depreciable lives for machinery and equipment generally range from three to 15 years . Net gains and losses related to asset disposals are recognized in earnings in the period in which the disposal occurs. Routine repairs, replacements and maintenance are expensed as incurred. We periodically evaluate whether current facts and circumstances indicate that the carrying value of depreciable long-lived assets may not be recoverable. If an asset, or logical grouping of assets, is determined to be impaired, the asset is written down to its fair value using discounted future cash flows and, if available, quoted market prices. Refer to Note 4 – “Plant Closures and Divestitures” for additional information. Goodwill and other intangible assets – Goodwill and other purchased intangible assets are included in the identifiable assets of the business segment to which they have been assigned. Goodwill is not amortized and is subject to an impairment test that we conduct annually or more frequently if a change in circumstances or the occurrence of events indicates that potential impairment exists. We perform an assessment of goodwill at the reporting unit level, utilizing a combination of an income approach, using a discounted cash flow methodology, and a market approach, by comparing the estimated fair value calculations of each reporting unit with its net book value. The discounted cash flow calculations are dependent on several subjective factors including the timing of future forecasted cash flows including future forecasted revenue growth rates, and the discount rate. If assumptions or estimates in the fair value calculations change or if future forecasted cash flows or future forecasted growth rates vary from what was planned, this may impact the impairment analysis. We performed an impairment test for goodwill for each of the reporting units using the above quantitative testing approach. Based on the evaluations performed, we determined that the fair value of each of the reporting units exceeded its carrying amount, and therefore, we determined that goodwill was no t impaired. Identifiable intangible assets, other than goodwill, are recorded at fair value. Identifiable intangible assets are amortized on a straight-line basis over their estimated useful lives. Deferred income taxes – Deferred tax assets and liabilities are recognized for future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. The effect on deferred tax assets and liabilities of a change in tax laws is recognized in earnings in the period the new laws are enacted. A valuation allowance is recorded to reduce the carrying amounts of deferred tax assets unless it is more likely than not that such assets will be realized. Leases – Lease arrangements are determined whether or not to be a lease at inception. Right-of-use (“ROU”) assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments. ROU lease liabilities are recognized based on the present value of the future minimum lease payments over the term of the lease as of the start date and may include consideration of certain adjustments including non-lease components. ROU assets are determined based on the determined ROU lease liability and may include the consideration of certain adjustments including initial direct costs, prepaid lease payments, lease incentives received, and non-lease components. The option to extend or terminate a lease is included in the determination of the ROU asset and lease liability only when it is reasonably certain that we will exercise that option. Asset retirement obligations – Asset retirement obligations are initially recorded at present value and are capitalized as part of the cost of the related long-lived asset when sufficient information is available to estimate present value. The capitalized costs are subsequently charged to depreciation expense over the estimated useful life of the related long-lived asset. The present value of the obligation is determined by calculating the discounted value of expected future cash flows and accretion expense is recorded each month to ultimately increase this obligation to fair value. We recognize asset retirement obligations for the removal and disposal of residues; dismantling of certain tanks required by governmental authorities; cleaning and dismantling costs for owned rail cars; cleaning costs for leased rail cars and barges; and site demolition, when required by governmental authorities or by contract. The following table describes changes to our asset retirement obligation liabilities: December 31, 2022 2021 (Dollars in millions) Asset retirement obligation at beginning of year $ 13.2 $ 19.8 Accretion expense 1.0 1.0 Revision in estimated cash flows 2.2 ( 0.3 ) Cash expenditures ( 1.0 ) ( 7.3 ) Balance at end of year $ 15.5 $ 13.2 Litigation and contingencies – Amounts associated with litigation and contingencies are accrued when management, after taking into consideration the facts and circumstances of each matter including any settlement offers, has determined that it is probable that a liability has been incurred and the amount of loss can be reasonably estimated. Legal costs for litigation are expensed as incurred with the exception of legal fees relating to the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, as amended (“CERCLA”), sites. Environmental liabilities – We accrue for remediation costs and penalties when the responsibility to remediate is probable and the amount of related cost is reasonably estimable. If only a range of potential liability can be estimated and no amount within the range is more probable than another, the accrual is recorded at the low end of that range. Remediation liabilities are discounted if the amount and timing of the cash disbursements are readily determinable. New Accounting Pronouncements In March 2022, the Financial Accounting Standards Board ("FASB") issued ASU No. 2022-01, "Derivatives and Hedging (Topic 815): Fair Value Hedging —Portfolio Layer Method." This ASU amends and simplifies existing guidance in order to allow companies to more accurately present the economic effects of risk management activities in financial statements. ASU No. 2022-01 is effective for periods beginning after December 15, 2022, and earlier adoption is permitted. The adoption of this ASU will not have a material impact on our financial statements as we principally utilize cash flow hedges.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2022
Business Combination and Asset Acquisition [Abstract]
Acquisitions	3. Acquisitions On October 31, 2022, we acquired substantially all of the assets of Gross & Janes Co. ("Gross & Janes") for $ 15.5 million in cash and we accounted for the transaction as a business combination. Gross & Janes was the largest independent supplier of untreated crossties in North America, with operations in Missouri, Arkansas and Texas. The business we acquired has been integrated into our RUPS segment and we believe the acquisition will strengthen our supply chain when procuring untreated crossties for our customers. Transaction costs, revenue and profit related to the acquisition were not material for the year ended December 31, 2022. The fair value of assets and liabilities acquired is set forth in the following table: (Dollars in millions) Accounts receivable $ 4.3 Inventory 7.4 Property, plant and equipment 4.5 Total assets acquired 16.2 Accounts payable and accrued liabilities 0.7 Net assets acquired $ 15.5

Plant Closures and Divestitures

Plant Closures and Divestitures	12 Months Ended
	Dec. 31, 2022
Discontinued Operations and Disposal Groups [Abstract]
Plant Closures and Divestitures	4. Plant Closures and Divestitures We have restructured our Carbon Materials and Chemicals (“CMC”) segment in order to concentrate our facilities in regions where we believe we hold key competitive advantages to better serve our global customers. These closure activities include: ▪ In February 2021, we sold our closed Follansbee, West Virginia coal tar distillation facility and we recorded a gain on sale of $ 5.7 million, consisting of $ 2.6 million from cash proceeds in addition to the assumption of certain liabilities by the buyer. ▪ In September 2020, we sold Koppers (Jiangsu) Carbon Chemical Company Limited ("KJCC"). Refer to Note 5 - "Discontinued Operations" for more details. ▪ In October 2018, we sold our closed Clairton, Pennsylvania coal tar distillation facility. In the first quarter of 2021, certain post-sale conditions were achieved and the buyer of the property released cash held in escrow to us resulting in a gain on sale of $ 1.8 million. Other closure and divestiture activity relates to our Railroad and Utility Products and Services (“RUPS”) segment, including: ▪ In March 2022, we sold our utility pole treating facility in Sweetwater, Tennessee and recorded a gain on sale of $ 2.5 million. ▪ In October 2021, we sold our closed Denver, Colorado crosstie treating facility and recorded a gain on sale of $ 23.4 million.

Discontinued Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2022
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations	5. Discontinued Operations On September 30, 2020, we sold KJCC to Fangda Carbon New Material Co., Ltd and C-Chem Co., Ltd., a subsidiary of Nippon Steel Chemical & Material Co., Ltd. (the “Buyers”). KJCC was located in Pizhou, Jiangsu Province, China and was a 75 percent-owned coal tar distillation company which was part of our CMC segment. The pre-tax gain on the sale of KJCC was $ 44.1 million and the after-tax gain on the sale was $ 35.8 million for the year ended December 31, 2020. On December 23, 2021 and March 31, 2022, the Buyers issued various claims, which, after negotiation, were settled in April 2022 for $ 0.9 million, of which our share is $ 0.7 million. These claims were paid out of amounts held in escrow and the remaining escrow amount of $ 1.5 million was fully released in August 2022. In the third quarter of 2022, we recorded a charge of $ 0.5 million related to a tax indemnity claim from the Buyers which was paid in the fourth quarter of 2022. The sale of KJCC represented a strategic shift that had a major effect on our operations and accordingly is classified as discontinued operations in our consolidated financial statements and notes. Net sales and operating loss from discontinued operations for the year ended December 31, 2020 consist of the following amounts: Year Ended December 31, 2020 (Dollars in millions) Net sales $ 31.6 Operating loss ( 5.0 ) The cash flows related to KJCC have not been restated in the Consolidated Statement of Cash Flows. Net cash inflows and outflows from discontinued operations for the year ended December 31, 2020 consist of the following amounts: Year Ended December 31, 2020 (Dollars in millions) Net cash provided by operating activities $ 0.7 Net cash used in investing activities ( 0.9 ) Effect of exchange rate changes on cash ( 0.5 ) Net decrease in cash and cash equivalents ( 0.7 )

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Measurements	6. Fair Value Measurements Carrying amounts and the related estimated fair values of our financial instruments as of December 31, 2022 are as follows: December 31, 2022 December 31, 2021 Fair Value Carrying Fair Value Carrying (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) $ 801.1 $ 825.3 $ 804.1 $ 789.1 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 and is measured from values received from financial institutions. 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 15 – "Debt") approximates carrying value due to the variable rate nature of this instrument.

Earnings and Dividends per Comm

Earnings and Dividends per Common Share	12 Months Ended
	Dec. 31, 2022
Earnings Per Share [Abstract]
Earnings and Dividends per Common Share	7. Earnings and Dividends per Common Share The computation of basic earnings per common share for the periods presented is based upon the weighted average number of common shares outstanding during the periods. The computation of diluted earnings per common share includes the effect of non-vested nonqualified stock options and stock units assuming such options and stock units were outstanding common shares at the beginning of the period. The effect of antidilutive securities is excluded from the computation of diluted loss per common share, if any. The following table sets forth the computation of basic and diluted earnings per common share: Year Ended December 31, 2022 2021 2020 (Dollars in millions, except share amounts, in thousands, and per share amounts) Net income attributable to Koppers $ 63.4 $ 85.2 $ 122.0 (Loss) gain on sale of discontinued operations, net of tax 0.0 , $ 0.1 and $( 7.4 ) ( 0.6 ) ( 0.2 ) 31.9 Income from continuing operations attributable to Koppers $ 64.0 $ 85.4 $ 90.1 Weighted average common shares outstanding: Basic 20,977 21,238 20,992 Effect of dilutive securities 336 687 382 Diluted 21,313 21,925 21,374 Earnings per common share – continuing operations: Basic earnings per common share $ 3.05 $ 4.02 $ 4.25 Diluted earnings per common share 3.00 3.90 4.17 Other data: Antidilutive securities excluded from computation of diluted 952 436 717 On February 15, 2023 , the board of directors declared a quarterly dividend of $ 0.06 per common share, payable on March 27, 2023 to shareholders of record as of March 10, 2023 .

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Stock-based Compensation	8. Stock-based Compensation We have outstanding stock-based compensation awards that were granted under the amended and restated 2005 Long-Term Incentive Plan (the “2005 LTIP”), the 2018 Long-Term Incentive Plan (the “2018 LTIP”) and the 2020 Long-Term Incentive Plan, as amended (the “2020 LTIP”). The 2005 LTIP, the 2018 LTIP and the 2020 LTIP are collectively referred to as the “LTIP”. The LTIP provides for the grant to eligible persons of stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance awards, dividend equivalents and other stock-based awards, which are collectively referred to as the “awards.” Restricted Stock Units and Performance Stock Units Under the LTIP, the board of directors grants restricted stock units and performance stock units to certain employee participants (collectively, the “stock units”). Compensation expense for non-vested stock units is recorded over the vesting period based on the fair value at the date of grant. The fair value of restricted stock units is the market price of the underlying common stock on the date of grant and the fair value of performance stock units is determined using a Monte Carlo valuation model. For grants to most employees, the restricted stock units vest in four equal annual installments. Restricted stock units that have one-year vesting periods are also issued as compensation under the LTIP to members of the board of directors and, from time to time, are issued to employees with vesting periods of two years or less. Performance stock units have vesting based upon a market condition. These performance stock units have multi-year performance objectives and a three-year period for vesting (if the applicable performance objective is achieved). The applicable performance objective is based on our total shareholder return relative to the Standard & Poor’s SmallCap 600 Materials Index. 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. We have the discretion to settle the awards in cash rather than shares, although we currently expect that all awards will be settled by the issuance of shares. We calculated the fair value of the performance stock unit awards on the date of the grant using assumptions listed below: January 2022 Grant January 2021 Grant March 2020 Grant Grant date price per share of stock $ 32.19 $ 29.84 $ 19.63 Expected dividend yield per share 0.00 % 0.00 % 0.00 % Expected volatility 66.90 % 68.70 % 45.60 % Risk-free interest rate 1.10 % 0.16 % 0.72 % Look-back period in years 3.00 3.00 2.83 Grant date fair value per share of stock $ 45.19 $ 41.50 $ 11.56 Dividends declared, if any, on our common stock during the period prior to vesting of the stock units are credited at equivalent value as additional stock units and become payable as additional common shares upon vesting. In the event of termination of employment, other than retirement, death or disability, any non-vested stock units are forfeited, including additional stock units credited from dividends. In the event of termination of employment due to retirement, death or disability, pro-rata vesting of the stock units over the service period will result. There are special vesting provisions for the stock units related to a change in control. The following table shows a summary of the performance stock units as of December 31, 2022: Performance Period Minimum Target Maximum 2021 – 2023 67,516 115,972 164,505 2022 – 2024 18,111 120,039 220,851 The minimum, target and maximum shares above reflect the impact from completed performance periods. Performance stock units granted in March 2020 for the 2020 – 2022 performance period did not meet the minimum performance criteria for any period and will not vest in March 2023. The following table shows a summary of the status and activity of non-vested stock awards for the year ended December 31, 2022: Restricted Performance Total Weighted Average Non-vested at January 1, 2022 505,905 474,166 980,071 $ 30.79 Granted 250,760 153,236 403,996 $ 35.78 Performance share adjustment 0 ( 124,932 ) ( 124,932 ) $ 25.24 Vested ( 202,716 ) ( 256,956 ) ( 459,672 ) $ 34.33 Forfeited ( 29,337 ) ( 9,501 ) ( 38,838 ) $ 27.93 Non-vested at December 31, 2022 524,612 236,013 760,625 $ 32.36 Stock Options Stock options to most executive officers vest and become exercisable in four equal annual installments. The stock options have a term of ten years . In the event of termination of employment, other than retirement, death or disability, any non-vested options are forfeited. In the event of termination of employment due to retirement, death or disability, pro-rata vesting of the options over the service period will result. There are special vesting provisions for the stock options related to a change in control. Compensation expense for non-vested stock options is recorded over the vesting period based on the fair value at the date of grant. We calculated the fair value of stock options on the date of grant using the Black-Scholes-Merton model and the assumptions listed below: January 2022 Grant January 2021 Grant March 2020 Grant March 2019 Grant Grant date price per share of stock $ 32.19 $ 29.84 $ 19.63 $ 26.63 Expected dividend yield per share 0.00 % 0.00 % 0.00 % 0.00 % Expected life in years 6.76 6.64 6.40 6.14 Expected volatility 54.50 % 54.80 % 42.85 % 39.44 % Risk-free interest rate 1.52 % 0.59 % 0.87 % 2.53 % Grant date fair value per share of stock $ 17.58 $ 15.79 $ 8.42 $ 11.29 Prior to February 2022, we had not declared a dividend since 2014. The expected life in years is based on historical exercise data of options previously granted by us. Expected volatility is based on the historical volatility of our common stock and the historical volatility of certain other similar public companies. The risk-free interest rate is based on U.S. Treasury bill rates for the expected life of the option. The following table shows a summary of the status and activity of stock options for the year ended December 31, 2022: Options Weighted Average Weighted Average Aggregate Intrinsic Outstanding at December 31, 2021 1,054,166 $ 26.89 Granted 98,108 $ 32.19 Expired ( 30,138 ) $ 38.21 Outstanding at December 31, 2022 1,122,136 $ 27.05 4.61 $ 5.5 Exercisable at December 31, 2022 843,475 $ 26.99 3.52 $ 4.7 Stock Compensation Expense Total stock-based compensation expense recognized under our LTIP and employee stock purchase plan for the three years ended December 31, 2022 is as follows: Year Ended December 31, 2022 2021 2020 (Dollars in millions) Stock-based compensation expense recognized: Selling, general and administrative expenses $ 13.2 $ 13.0 $ 11.3 Less related income tax benefit 4.4 3.7 2.2 Decrease in net income attributable to Koppers $ 8.8 $ 9.3 $ 9.1 Intrinsic value of exercised stock options $ 0.0 $ 2.2 $ 0.0 Cash received from the exercise of stock options $ 0.0 $ 2.3 $ 0.0 As of December 31, 2022 , total future compensation expense related to non-vested stock-based compensation arrangements totaled $ 18.4 million and the weighted-average period over which this expense is expected to be recognized is approximately 25 months .

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2022
Segment Reporting [Abstract]
Segment Information	9. Segment Information We have three reportable segments: Railroad and Utility Products and Services, Performance Chemicals and Carbon Materials and Chemicals. 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 sells treated and untreated wood products, manufactured products and services primarily to the railroad and public 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 and the manufacture of rail joint bars. Utility products include transmission and distribution poles and pilings. The segment also operates a railroad services business that conducts engineering, design, repair and inspection services for railroad bridges, a business related to the recovery of used crossties and utility poles and a business related to the inspection of utility poles. Our PC segment develops, manufactures, and markets wood preservation chemicals and wood treatment technologies and services a diverse range of end-markets including infrastructure, residential 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 used in the production of aluminum and steel in electric arc furnaces. 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, acquisition-related charges, mark-to-market commodity hedging, gain/loss on sale of assets and non-cash LIFO 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. 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. The following table sets forth certain sales and operating data by segment for the periods indicated: Year Ended December 31, 2022 2021 2020 (Dollars in millions) Revenues from external customers: Railroad and Utility Products and Services $ 788.3 $ 729.9 $ 759.1 Performance Chemicals 579.9 503.3 526.3 Carbon Materials and Chemicals (a) 612.3 445.4 383.7 Total $ 1,980.5 $ 1,678.6 $ 1,669.1 Intersegment revenues: Performance Chemicals $ 22.2 $ 15.9 $ 13.7 Carbon Materials and Chemicals 74.3 75.3 78.7 Total $ 96.5 $ 91.2 $ 92.4 Depreciation and amortization expense: Railroad and Utility Products and Services $ 22.3 $ 22.3 $ 20.1 Performance Chemicals 15.3 17.9 18.1 Carbon Materials and Chemicals (b) 18.5 17.5 15.9 Total $ 56.1 $ 57.7 $ 54.1 Adjusted EBITDA: Railroad and Utility Products and Services $ 53.6 $ 45.4 $ 65.3 Performance Chemicals 75.5 101.8 100.7 Carbon Materials and Chemicals 99.0 76.3 45.0 Items excluded from the determination of segment Impairment, restructuring and plant closure ( 1.1 ) ( 4.2 ) ( 15.7 ) Gain on sale of assets 2.5 31.2 0.0 LIFO (expense) benefit ( 25.6 ) ( 28.2 ) 13.7 Mark-to-market commodity hedging (losses) gains ( 6.5 ) ( 3.8 ) 9.2 Inventory adjustment (c) ( 1.1 ) 0.0 0.0 Pension settlement 0.0 0.0 ( 0.1 ) Discretionary incentive (d) 0.0 0.0 ( 3.0 ) Interest expense ( 44.8 ) ( 40.5 ) ( 48.9 ) Depreciation and amortization ( 56.1 ) ( 57.7 ) ( 54.1 ) Depreciation in impairment and restructuring charges 0.0 ( 0.7 ) ( 2.0 ) Income tax provision ( 31.6 ) ( 34.5 ) ( 21.0 ) Discontinued operations ( 0.6 ) ( 0.2 ) 31.9 Net income $ 63.2 $ 84.9 $ 121.0 Capital expenditures: Railroad and Utility Products and Services $ 47.2 $ 62.0 $ 31.3 Performance Chemicals 10.6 17.7 12.1 Carbon Materials and Chemicals (e) 45.7 42.9 24.8 Corporate 1.8 2.4 1.6 Total $ 105.3 $ 125.0 $ 69.8 (a) Revenue excludes KJCC discontinued operations of $ 31.6 million for the year ended December 31, 2020. (b) Depreciation and amortization expense excludes KJCC discontinued operations of $ 0.6 million for the year ended December 31, 2020. (c) Represents fair value step-up on inventory acquired in a business acquisition as described in Note 3 – "Acquisitions". (d) Represents a one-time employee incentive associated with the sale of KJCC as described in Note 5 – "Discontinued Operations". (e) Capital expenditures includes KJCC discontinued operations of $ 0.6 million for the year ended December 31, 2020. The following table sets forth tangible and intangible assets allocated to each of our segments as of the dates indicated: December 31, 2022 2021 (Dollars in millions) Segment assets: Railroad and Utility Products and Services $ 660.8 $ 594.1 Performance Chemicals 516.9 586.9 Carbon Materials and Chemicals 500.5 447.1 Segment assets 1,678.2 1,628.1 Prepaid insurance and other assets 16.0 16.5 Property, plant and equipment, net 6.8 6.6 Operating lease right-of-use assets 10.4 10.7 Total $ 1,711.4 $ 1,661.9 Goodwill: Railroad and Utility Products and Services $ 120.6 $ 120.9 Performance Chemicals 173.4 175.1 Total $ 294.0 $ 296.0 Revenues and Long-lived Assets by Geographic Area Year Revenue Long-lived (Dollars in millions) United States 2022 $ 1,271.1 $ 902.9 2021 1,134.2 857.3 2020 1,170.1 832.0 Australasia 2022 283.0 73.8 2021 230.6 78.9 2020 194.3 82.0 Europe 2022 248.9 67.6 2021 195.8 63.3 2020 162.3 83.2 Other countries 2022 177.5 18.6 2021 118.0 19.3 2020 142.4 18.5 Total (a) 2022 $ 1,980.5 $ 1,062.9 2021 $ 1,678.6 $ 1,018.8 2020 $ 1,669.1 $ 1,015.7 (a) Revenue excludes KJCC discontinued operations of $ 31.6 million for the year ended December 31, 2020. Revenues by geographic area in the above table are attributed by the destination country of the sale. Revenues from non-U.S. countries totaled $ 709.4 million in 2022, $ 544.4 million in 2021 and $ 499.0 million in 2020. Segment Revenues for Significant Product Lines Year Ended December 31, 2022 2021 2020 (Dollars in millions) Railroad and Utility Products and Services: Railroad treated products $ 457.4 $ 414.4 $ 405.1 Utility poles 227.9 228.0 241.7 Railroad infrastructure services 61.8 56.0 63.5 Rail joints 28.0 22.7 20.3 Other products 13.2 8.8 28.6 788.3 729.9 759.1 Performance Chemicals: Wood preservative products 561.2 489.1 510.7 Other products 18.7 14.2 15.6 579.9 503.3 526.3 Carbon Materials and Chemicals: Pitch and related products 390.7 260.3 230.9 Phthalic anhydride and other chemicals 109.1 75.6 66.4 Creosote and distillates 62.9 52.1 40.0 Naphthalene 36.0 27.1 19.7 Other products 13.6 30.3 26.7 612.3 445.4 383.7 Total (a) $ 1,980.5 $ 1,678.6 $ 1,669.1 (a) Revenue excludes KJCC discontinued operations of $ 31.6 million for the year ended December 31, 2020.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes Income Tax Provision Components of our income tax provision are as follows: Year Ended December 31, 2022 2021 2020 (Dollars in millions) Current: Federal $ 0.0 $ ( 1.5 ) $ 0.8 State 0.6 0.9 0.7 Foreign 28.4 18.2 11.1 Total current tax provision 29.0 17.6 12.6 Deferred: Federal 0.2 10.6 6.1 State ( 0.6 ) 1.1 1.6 Foreign 3.0 5.2 0.7 Total deferred tax provision 2.6 16.9 8.4 Total income tax provision $ 31.6 $ 34.5 $ 21.0 Income before income taxes from foreign operations for 2022, 2021 and 2020 was $ 106.8 million, $ 71.8 million and $ 52.4 million, respectively. The provision for income taxes is reconciled with the federal statutory income tax rate as follows: Year Ended December 31, 2022 2021 2020 Federal income tax rate 21.0 % 21.0 % 21.0 % Foreign earnings taxed at different rates 8.7 4.3 2.9 GILTI inclusion, net of foreign tax credits 1.7 0.2 4.0 Valuation allowance adjustments 0.9 1.9 ( 12.1 ) Deferred tax adjustments 0.0 ( 0.2 ) ( 2.2 ) Change in tax contingency reserves ( 0.1 ) ( 1.1 ) ( 0.2 ) State income taxes, net of federal tax benefit ( 0.2 ) 2.1 2.2 Other 1.1 0.6 3.5 33.1 % 28.8 % 19.1 % For each of the three years ended December 31, 2022, 2021 and 2020 , we have recorded valuation allowance adjustments related to the value of certain deferred tax assets. In 2022, we recorded $ 0.9 million of adjustments to our valuation allowance for certain foreign and state tax deferred tax assets. In 2021, we recorded a $ 3.3 million valuation allowance against net deferred tax assets of our United Kingdom entities as a result of a recent history of pre-tax losses and the reversal of a deferred tax liability associated with a defined benefit pension plan. In 2020, the valuation allowance adjustment was favorably impacted by our ability to utilize interest expense deduction carry forwards in the United States. As of December 31, 2019, we had recorded a cumulative valuation allowance totaling $ 13.3 million for disallowed interest expense deductions due to the uncertainly of when we could utilize the carry forward amounts. During 2020, new regulations impacted our interest expense limitation in our 2018 and 2019 U.S. tax returns. In March 2020, the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”) was enacted and a provision of the CARES Act increased the allowable business interest expense deduction to 50 percent of adjusted taxable income retroactively to January 1, 2019. This combined with other newly released regulations favorably impacted our calculation of adjusted taxable income. After application of these new regulations, the limitation of our interest expense deduction was significantly reduced when compared to the same calculations under the previous regulations. Due to these changes, in the year ended December 31, 2020 we recorded an income tax benefit of $ 13.3 million, to adjust a previously recorded valuation allowance for disallowed interest expense deductions that were eligible for carry forward as we determined that we would be able to fully utilize these disallowed interest expense deductions. Taxes Excluded from Net Income Attributable to Koppers The amount of deferred income tax benefit (expense) included in comprehensive income but excluded from net income attributable to Koppers relates primarily to adjustments to copper swap contracts of $ 6.1 million, $ 0.5 million, and $( 12.6 ) million for the years ended December 31, 2022, 2021 and 2020, respectively. The amount of deferred income tax benefit (expense) included in comprehensive income but excluded from net income attributable to Koppers relates to adjustments to reflect the unfunded status of employee post-retirement benefit plans of $( 0.5 ) million, $ 1.3 million, and $ 0.4 million for the years ended December 31, 2022, 2021 and 2020, respectively. Deferred Tax Assets and Liabilities Deferred income taxes reflect the net tax effects of differences between the carrying amounts of assets and liabilities for financial reporting purposes and for income tax purposes. Significant components of our deferred tax assets and liabilities are as follows: Year Ended December 31, 2022 2021 (Dollars in millions) Deferred tax assets: Federal and state tax loss carryforwards, expiring in 2023 to 2042 $ 22.6 $ 24.4 Tax credits 17.4 17.5 Reserves, including insurance and environmental 9.3 9.0 Pension and other post-retirement benefits obligations 8.2 9.6 Foreign tax loss carryforwards 6.6 7.4 Accrued employee compensation 6.5 7.1 Interest disallowance 6.4 0.0 Asset retirement obligations 5.3 4.5 Inventory 4.6 5.9 Other 4.6 3.3 Valuation allowance ( 43.8 ) ( 44.5 ) Total deferred tax assets 47.7 44.2 Deferred tax liabilities: Tax over book depreciation and amortization 52.3 44.0 Gain on derivative contracts 0.7 14.3 Other 4.5 4.3 Total deferred tax liabilities 57.5 62.6 Net deferred tax liabilities $ ( 9.8 ) $ ( 18.4 ) As a result of the Tax Act and the one-time mandatory transition tax, all previously unremitted earnings for which a U.S. deferred tax liability had not been accrued have now been subject to U.S. tax. As of December 31, 2022 , there was approximately $ 518 million of such unremitted earnings. Substantially all unremitted earnings will remain indefinitely invested in our foreign subsidiaries for the foreseeable future unless we can remit any earnings as a dividend in a tax-free manner. In the event any earnings are remitted as a dividend with a tax cost due to currency gains or losses, state taxes, or foreign withholding taxes, we estimate that we will not incur significant additional taxes on those potential remittances. Management evaluated the ability to realize the deferred tax assets that are related to our domestic and international operations. In assessing the need for a valuation allowance, management considered all positive and negative evidence related to the realization of our net deferred tax assets. We believe that we will be in a taxable income position in the foreseeable future and we will have sufficient taxable income to utilize deferred tax assets that do not have a valuation allowance related to our domestic and international operations. A valuation allowance is necessary when it is more likely than not that a deferred tax asset will not be realized. Certain deferred tax assets reflected above are not expected to be realized and a valuation allowance has been provided for them. Valuation allowances are recorded to offset the following deferred tax assets: December 31, 2022 2021 State temporary differences, net operating losses and tax credits $ 19.4 $ 19.2 Federal foreign tax credits 16.1 16.1 Foreign temporary differences, net operating losses and capital losses 8.3 9.1 Federal temporary differences 0.0 0.1 Total valuation allowances $ 43.8 $ 44.5 Unrecognized Tax Benefits A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: December 31, 2022 2021 2020 (Dollars in millions) Balance at beginning of year $ 1.5 $ 2.5 $ 2.1 Additions based on tax provisions related to the current year 0.1 0.1 0.2 Additions for tax provisions of prior years 0.0 0.0 0.5 Reductions resulting from a lapse in the statute of limitations ( 0.2 ) ( 1.1 ) ( 0.3 ) Balance at end of year $ 1.4 $ 1.5 $ 2.5 As of December 31, 2022 and 2021 , the total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate, was approximately $ 1.4 million and $ 1.5 million, respectively. We recognize interest expense and any related penalties from unrecognized tax benefits in income tax expense. For the year ended December 31, 2022 , we recognized $( 0.1 ) million in interest and penalties. As of December 31, 2022 and 2021 , we had accrued interest and penalties of approximately $ 0.3 million and $ 0.4 million, respectively. We do not anticipate significant increases or decreases to the amount of unrecognized tax benefits within the next twelve months. Koppers Holdings and its subsidiaries 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 before 2017.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2022
Inventory Disclosure [Abstract]
Inventories	11. Inventories Inventories as of December 31, 2022 and December 31, 2021 were as follows: December 31, 2022 2021 (Dollars in millions) Raw materials $ 318.5 $ 266.8 Work in process 10.2 12.6 Finished goods 130.4 112.1 459.1 391.5 Less revaluation to LIFO 103.4 77.7 Inventories, net $ 355.7 $ 313.8

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	12. Property, Plant and Equipment Property, plant and equipment as of December 31, 2022 and December 31, 2021 were as follows: December 31, 2022 2021 (Dollars in millions) Land $ 15.0 $ 15.2 Buildings 80.3 75.8 Machinery and equipment 924.1 836.8 1,019.4 $ 927.8 Less accumulated depreciation 462.1 438.7 Property, plant and equipment, net $ 557.3 $ 489.1 Depreciation expense for the years ended December 31, 2022, 2021 and 2020 amounted to $ 41.2 million, $ 39.4 million and $ 33.7 million, respectively. Depreciation expense excludes KJCC discontinued operations of $ 0.6 million for the year ended December 31, 2020. Impairments – We did no t incur impairment charges in 2022, 2021 and 2020 .

Goodwill and Other Identifiable

Goodwill and Other Identifiable Intangible Assets	12 Months Ended
	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Identifiable Intangible Assets	13. Goodwill and Other Identifiable Intangible Assets The change in the carrying amount of goodwill attributable to each reporting unit for the years ended December 31, 2022 and December 31, 2021 was as follows: Performance Chemicals Railroad Products and Services Utility Total (Dollars in millions) Balance at December 31, 2020 $ 176.7 $ 41.1 $ 80.0 $ 297.8 Currency translation ( 1.6 ) 0.0 ( 0.2 ) ( 1.8 ) Balance at December 31, 2021 $ 175.1 $ 41.1 $ 79.8 $ 296.0 Currency translation ( 1.7 ) ( 0.1 ) ( 0.2 ) ( 2.0 ) Balance at December 31, 2022 $ 173.4 $ 41.0 $ 79.6 $ 294.0 Goodwill represents the excess of the cost over the fair value of acquired identifiable tangible and intangible assets and liabilities assumed from businesses acquired. Goodwill is tested for impairment at the reporting unit level annually in the fourth quarter or more frequently if a change in circumstances or the occurrence of events indicates that potential impairment exists, using discounted cash flows. We performed a quantitative assessment of goodwill at the reporting unit level, utilizing a combination of an income approach, using a discounted cash flow methodology, and a market approach, by comparing the estimated fair value calculations of each reporting unit with its net book value. The discounted cash flow calculations are dependent on several subjective factors including the timing of future forecasted cash flows, including forecasted future growth rates such as revenue and the discount rate. We determined that the estimated fair values exceeded the carrying values of all the reporting units, and accordingly, there was no impairment of goodwill incurred for each of the three years ended December 31, 2022. Our identifiable intangible assets are being amortized over their estimated useful lives and are summarized below: December 31, 2022 2021 Estimated Weighted Gross Accumulated Net Gross Accumulated Net (Dollars in millions) Customer contracts 9 to 18 9.0 $ 224.9 $ 110.5 $ 114.4 $ 226.9 $ 97.6 $ 129.3 Technology 4 to 12 3.6 26.4 26.0 0.4 26.5 25.9 0.6 Trademarks 2 to 18 11.0 7.7 6.5 1.2 7.6 6.4 1.2 Supply contracts 10 0.0 2.4 2.4 0.0 2.4 2.4 0.0 Non-compete 12 1.8 1.6 1.5 0.1 1.7 1.3 0.4 Total 8.9 $ 263.0 $ 146.9 $ 116.1 $ 265.1 $ 133.6 $ 131.5 In 2022, the gross carrying value of identifiable intangible assets decreased by a net $ 2.1 million, primarily due to foreign exchange translation. Total amortization expense related to these identifiable intangible assets was $ 14.9 million, $ 18.3 million and $ 19.8 million for the years ended December 31, 2022, 2021 and 2020 , respectively. Estimated amortization expense for the next five years is summarized below: Estimated (Dollars in millions) 2023 $ 14.4 2024 14.2 2025 13.7 2026 12.4 2027 12.0

Pensions and Post-Retirement Be

Pensions and Post-Retirement Benefit Plans	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
Pensions and Post-Retirement Benefit Plans	14. 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. These plans are maintained and contributions are made in accordance with the Employee Retirement Income Security Act of 1974 (“ERISA”), local statutory law or as determined by the board of directors. The defined benefit pension plans generally provide benefits based upon years of service and compensation. Pension plans are funded except for three domestic non-qualified defined benefit pension plans for certain key executives. In the United States, all qualified and two of the non-qualified defined benefit pension plans for salaried and hourly employees have been closed to new participants and have been frozen. Accordingly, these pension plans no longer accrue additional years of service or recognize future increases in compensation for benefit purposes. The defined contribution plans generally provide retirement assets to employee participants based upon employer and employee contributions to the participant’s individual investment account. We also provide retiree medical insurance coverage to certain U.S. employees and a life insurance benefit to most U.S. employees. For salaried employees, the retiree medical and retiree insurance plans have been closed to new participants. Expense related to defined contribution plans totaled $ 8.4 million, $ 9.1 million and $ 8.4 million for the years ended December 31, 2022, 2021 and 2020, respectively. Net periodic pension costs for 2022, 2021 and 2020 were as follows: Year Ended December 31, Pension Benefits Other Benefits 2022 2021 2020 2022 2021 2020 (Dollars in millions) Service cost $ 1.2 $ 1.5 $ 1.4 $ 0.0 $ 0.1 $ 0.1 Interest cost 5.6 5.2 6.4 0.3 0.3 0.3 Expected return on plan assets ( 7.7 ) ( 7.4 ) ( 7.9 ) 0.0 0.0 0.0 Amortization of net loss (gain) 1.8 1.4 1.7 ( 0.1 ) 0.0 ( 0.2 ) Settlements and curtailments 0.0 0.0 0.1 0.0 0.0 0.0 Net periodic benefit cost $ 0.9 $ 0.7 $ 1.7 $ 0.2 $ 0.4 $ 0.2 The change in the funded status of the pension and post-retirement plans as of December 31, 2022 and December 31, 2021 is as follows: Year Ended December 31, Pension Benefits Other Benefits 2022 2021 2022 2021 (Dollars in millions) Change in benefit obligation: Benefit obligation at beginning of year $ 219.6 $ 233.3 $ 9.8 $ 10.5 Service cost 1.2 1.5 0.0 0.1 Interest cost 5.6 5.2 0.3 0.3 Actuarial gains ( 51.8 ) ( 9.0 ) ( 3.4 ) ( 0.6 ) Settlements ( 1.0 ) 0.0 0.0 0.0 Currency translation ( 5.8 ) ( 0.6 ) 0.0 0.0 Benefits paid ( 10.8 ) ( 10.8 ) ( 0.7 ) ( 0.5 ) Benefit obligation at end of year 157.0 219.6 6.0 9.8 Change in plan assets: Fair value of plan assets at beginning of year 190.0 208.0 0.0 0.0 Actual return on plan assets ( 46.1 ) ( 8.9 ) 0.0 0.0 Employer contribution 0.9 2.3 0.7 0.5 Settlements ( 1.0 ) 0.0 0.0 0.0 Currency translation ( 5.6 ) ( 0.6 ) 0.0 0.0 Benefits paid ( 10.8 ) ( 10.8 ) ( 0.7 ) ( 0.5 ) Fair value of plan assets at end of year 127.4 190.0 0.0 0.0 Funded status of the plan $ ( 29.6 ) $ ( 29.6 ) $ ( 6.0 ) $ ( 9.8 ) In 2022, the net actuarial gain of $ 51.8 million is due principally to the increase of 275 basis points in the discount rate used to measure the benefit obligation as of December 31, 2022 compared to the prior year. The actual return on plan assets was negative in 2022 primarily due to investment losses of $ 32.3 million in the US defined benefit pension plan and the revaluation decrease of $ 13.6 million in the bulk annuity insurance policy related to our defined benefit pension plan in the United Kingdom. As of December 31, 2022 , the fair value of the bulk annuity insurance policy of $ 31.6 million is based on the calculated pension benefit obligation and is classified as Level 3 within the fair value hierarchy. As the calculated pension benefit obligation decreased due to an increase in the discount rate, there was a commensurate decrease in the value of the bulk annuity insurance policy. During 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 our defined benefit pension plan in the United Kingdom, but the plan still retains full legal responsibility to pay the benefits to the members of the plan 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 was substantially completed in late 2022 and by late 2023, the pension obligation is expected to be irrevocably settled. Upon that event, we will recognize a pre-tax pension settlement loss of approximately $ 20 million. This pension plan has a benefit obligation of $ 32.6 million and plan assets of $ 31.6 million as of December 31, 2022. Plan Data Year Ended December 31, Pension Benefits Other Benefits 2022 2021 2022 2021 (Dollars in millions) Amounts recognized in the balance sheet Noncurrent assets $ 0.6 $ 0.8 $ 0.0 $ 0.0 Current liabilities 1.0 1.0 0.5 0.6 Noncurrent liabilities 29.2 29.4 5.5 9.2 Pension plans with projected benefit obligations Benefit obligation $ 154.4 $ 215.7 Fair value of plan assets 124.2 185.3 Pension plans with accumulated benefit Accumulated benefit obligation $ 154.2 $ 215.5 Fair value of plan assets 124.2 185.3 The measurement date for all pension and post-retirement assets and obligations is December 31 for each respective year. The accumulated benefit obligation for all defined benefit pension plans as of December 31, 2022 and December 31, 2021 was $ 156.8 million and $ 219.1 million, respectively. Expected Contributions for the 2023 Fiscal Year Our expected contributions for 2023 are estimated to be $7 .0 million for pension plans and $ 0.6 million for other benefit plans. Projected Benefit Payments Benefit payments for pension benefits, which are primarily funded by the pension plan assets, and other benefits, which are funded by general corporate assets, are expected to be paid as follows: Pension Benefits Other Benefits (Dollars in millions) 2023 $ 11.6 $ 0.5 2024 11.3 0.5 2025 11.8 0.5 2026 11.3 0.5 2027 11.2 0.5 Next five years 57.9 2.4 Weighted-Average Assumptions December 31, Pension Benefits Other Benefits 2022 2021 2022 2021 Discount rate 5.42 % 2.67 % 5.58 % 2.97 % Expected return on plan assets 4.65 3.91 Rate of compensation increase 3.13 3.00 Initial medical trend rate 5.40 5.40 Basis for the Selection of the Long-Term Rate of Return on Assets The long-term rate of return on assets assumption was determined by using the plan’s asset allocation as described in the plan’s investment policy and modeling a distribution of compound average returns over a time horizon. The model uses asset class return, variance, and correlation assumptions to produce the expected return. The return assumptions used forward looking gross returns influenced by the current bond yields, corporate bond spreads and equity risk premiums based on current market conditions. In general, the long-term rate of return is the sum of the portion of total assets in each asset class multiplied by the expected return for that class, adjusted for expected expenses to be paid from the assets. To develop the expected long-term rate of return on assets assumption, we considered the historical returns and the future expectations for returns for each asset class, as well as the target asset allocation of the pension portfolio. Investment Strategy The weighted average asset allocation for our pension plans as of December 31 by asset category is as follows: December 31, 2022 2021 Debt securities 52 % 49 % Equity securities 20 21 Other 28 30 100 % 100 % Our investment strategy for our pension plans is to maintain an adequate level of diversification, to reduce interest rate and market risk and to provide adequate liquidity to meet immediate and future benefit payment requirements. Our overall investment strategy is to achieve a mix of growth seeking assets, principally U.S. and international public company equity securities and income generating assets, principally debt securities, real estate and cash. For all pension plans not engaged in a buy-out process, we target an allocation of 30 percent to 40 percent growth seeking assets and 60 percent to 70 percent income generating assets on an overall basis. We utilize investment managers to assist in identifying and monitoring investments that meet these allocation criteria. With respect to the U.S. defined benefit plan, we have implemented a strategy of reallocating pension assets from growth seeking assets to income generating assets as certain funded status levels are reached. All assets are invested in pooled or commingled investment vehicles with the exception of the insurance annuity contract. Our interest in these investment vehicles is expressed as a unit of account with a value per unit that is the result of the accumulated values of the underlying investments. Equity securities held within these investment vehicles are typically priced on a daily basis using the closing market price from the exchange through which the security is traded. Debt securities held within these investment vehicles are typically priced on a daily basis by independent pricing services. Certain investments are valued using the net asset value (“NAV”) practical expedient and have not been categorized in the fair value hierarchy but are included to reconcile the fair value hierarchy to the total fair value of plan assets. The fair value of real estate investments is either priced through a listing on an exchange or are subject to periodic appraisals. The following tables set forth by level, our pension plan assets at fair value, within the fair value hierarchy, as of December 31, 2022 and December 31, 2021: December 31, 2022 Quoted prices in Significant Significant Total (Dollars in millions) U.S. equity securities $ 0.0 $ 4.9 $ 0.0 $ 4.9 International equity securities 0.0 11.1 0.0 11.1 U.S. debt securities 0.0 39.2 0.0 39.2 International debt securities 0.0 2.6 0.0 2.6 Insurance annuity contract and other 0.0 0.5 31.5 32.0 Cash and cash equivalents 0.0 1.6 0.0 1.6 $ 0.0 $ 59.9 $ 31.5 $ 91.4 Investments measured at NAV (a) 36.0 Total assets at fair value $ 127.4 (a) The fair value amounts presented in the table above are intended to permit reconciliations of the fair value hierarchy to the total plan assets. December 31, 2021 Quoted prices in Significant Significant Total (Dollars in millions) U.S. equity securities $ 0.0 $ 7.9 $ 0.0 $ 7.9 International equity securities 0.0 17.9 0.0 17.9 U.S. debt securities 0.0 64.9 0.0 64.9 International debt securities 0.0 3.6 0.0 3.6 Other investments 0.0 0.6 52.3 52.9 Cash and cash equivalents 0.0 2.1 0.0 2.1 $ 0.0 $ 97.0 $ 52.3 $ 149.3 Investments measured at NAV (a) 40.7 Total assets at fair value $ 190.0 (a) The fair value amounts presented in the table above are intended to permit reconciliations of the fair value hierarchy to the total plan assets. Incentive Plan We have short-term management incentive plans that pay cash bonuses if certain company performance goals are met. Expenses incurred for these plans were $ 12.6 million in 2022 , $ 14.9 million in 2021 and $ 17.3 million in 2020 .

Debt

Debt	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Debt	15. Debt Debt as of December 31, 2022 and December 31, 2021 was as follows: December 31, Weighted Maturity 2022 2021 Term Loan - - $ 0.0 $ 2.0 Revolving Credit Facility - - 0.0 287.1 Revolving Credit Facility 6.72 % 2027 325.3 0.0 Senior Notes due 2025 6.00 % 2025 500.0 500.0 Total debt 825.3 789.1 Less short-term debt and current maturities of 0.0 2.0 Less unamortized debt issuance costs 7.6 5.6 Long-term debt $ 817.7 $ 781.5 Revolving Credit Facility In June 2022, we entered into an $ 800.0 million revolving credit agreement (the “Credit Facility”) with a consortium of banks which replaced our previous $ 600.0 million senior secured revolving credit facility and $ 100.0 million senior secured term loan facility (the latter having been fully repaid as of March 31, 2022). The Credit Facility also provides for 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 maturity date of the Credit Facility is currently June 17, 2027 but is subject to a springing maturity in the event the 2025 Notes (as defined below) are not repurchased, redeemed or refinanced prior to November 15, 2024. 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 their material domestic subsidiaries. The Credit Facility contains certain covenants that limit Koppers Inc. and its restricted subsidiaries, including, without limitation, limitations on additional indebtedness, liens, dividends, investments, acquisitions, subsidiary and certain other distributions, asset sales, transactions with affiliates and modifications to material documents, including organizational documents. In addition, such covenants give rise to events of default upon the failure by Koppers Inc. and its restricted subsidiaries to meet certain financial ratios. As of December 31, 2022 , we had $ 412.0 million of unused revolving credit availability for working capital purposes after restrictions from certain letter of credit commitments and other covenants. As of December 31, 2022 , $ 7.8 million of commitments were utilized by outstanding letters of credit. Senior Notes due 2025 Koppers Inc.'s $ 500 million Senior Notes due 2025 ("the "2025 Notes") are senior obligations of Koppers Inc., and are unsecured and are guaranteed by Koppers Holdings Inc. and certain of Koppers Inc.’s domestic subsidiaries. The 2025 Notes pay interest semi-annually in arrears on February 15 and August 15 and will mature on February 15, 2025 unless earlier redeemed or repurchased. We were entitled to redeem all or a portion of the 2025 Senior Notes at a redemption price of 101.5 percent of principal value as of February 15, 2022 until April 15, 2023 when the 2025 Notes are redeemable at principal value. The indenture governing the 2025 Senior Notes includes customary covenants that restrict, among other things, the ability of Koppers Inc. and its restricted subsidiaries to incur additional debt, pay dividends or make certain other restricted payments, incur liens, merge or sell all or substantially all of the assets of Koppers Inc. or its subsidiaries or enter into various transactions with affiliates. Debt Maturities and Deferred Financing Costs At December 31, 2022 the aggregate debt maturities for the next five years are as follows: (Dollars in millions) 2023 $ 0.0 2024 0.0 2025 500.0 2026 0.0 2027 325.3 Total debt $ 825.3 Unamortized debt issuance costs (net of accumulated amortization of $ 14.9 million and $ 12.1 million at December 31, 2022 and 2021 , respectively) were $ 7.6 million and $ 5.6 million at December 31, 2022 and 2021 , respectively, and are included as a deduction from the carrying amount of long-term debt.

Leases

Leases	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Leases	16. Leases We recognize lease obligations and associated right-of-use assets for existing non-cancelable leases. We have non-cancelable operating leases primarily associated with railcars, office and manufacturing facilities, storage tanks, ships, production equipment and vehicles. Many of our leases include both lease (e.g., fixed rent) and non-lease components (e.g., maintenance and services). For certain asset classes such as railcars, storage tanks and ships, we have separated the lease and non-lease components based on the estimated stand-alone price for each component. For the remaining asset classes, we have elected to account for these components as a single lease component. In addition, we exclude leases expiring within twelve months from balance sheet recognition. Many of our leases include one or more options to renew. We evaluate renewal options at the lease commencement date and regularly thereafter to determine if we are reasonably certain to exercise the option, in which case we include the renewal period in our lease term. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on information available to determine the present value of the lease payments. Lease expense for operating leases is recognized on a straight-line basis over the lease term. Variable lease expense is recognized in the period in which the obligation for those payments is incurred. Operating lease costs were $ 29.3 million and $ 30.2 million and variable lease costs were $ 3.3 million and $ 3.3 million during the years ended December 31, 2022 and 2021, respectively. The following table presents information about the amount and timing of cash flows arising from our operating leases as of December 31, 2022: (Dollars in millions) 2023 $ 26.2 2024 22.3 2025 17.1 2026 12.3 2027 10.0 Thereafter 20.6 Total lease payments $ 108.5 Less: Interest ( 21.7 ) Present value of lease liabilities $ 86.8 Supplemental consolidated balance sheet information related to leases is as follows: December 31, 2022 2021 (Dollars in millions) Operating leases: Operating lease right-of-use assets $ 86.3 $ 91.2 Current operating lease liabilities $ 20.5 $ 21.3 Operating lease liabilities 66.3 70.3 Total operating lease liabilities $ 86.8 $ 91.6 Weighted average remaining lease term, in years 5.6 5.8 Weighted average discount rate 7.2 % 7.4 %

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	17. Derivative Financial Instruments We utilize derivative instruments to manage exposures to risks that have been identified and measured and are capable of being controlled. The primary risks that we manage by using derivative instruments are commodity price risk associated with copper and foreign currency exchange risk associated with a number of currencies, principally the U.S. dollar, the Euro and British pounds. 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 2024. 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. 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. ASC Topic 815-10, “Derivatives and Hedging,” requires companies to recognize all derivative instruments as either assets or liabilities at fair value in the balance sheet. Derivative instruments’ fair value is determined using significant other observable inputs, or Level 2 in the fair value hierarchy. In accordance with ASC Topic 815-10, we designate certain of our commodity swaps as cash flow hedges of forecasted purchases of commodities. 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. For those commodity swaps where hedge accounting is not elected, the fair value of the commodity swap is recognized as an asset or liability in the consolidated balance sheet and the related 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 December 31, 2022 and December 31, 2021, we had outstanding copper swap contracts of the following amounts: Units Outstanding (in Pounds) Net Fair Value - Asset December 31, December 31, 2022 2021 2022 2021 (Amounts in millions) Cash flow hedges 21.3 29.0 $ 2.5 $ 53.8 Not designated as hedges 6.0 6.1 0.6 7.1 Total 27.3 35.1 $ 3.1 $ 60.9 As of December 31, 2022 and December 31, 2021, the fair value of the outstanding copper swap contracts is recorded in the balance sheet as follows: December 31, 2022 2021 (Dollars in millions) Derivative contracts $ 3.4 $ 60.9 Accrued liabilities ( 0.3 ) 0.0 Net asset on balance sheet $ 3.1 $ 60.9 Accumulated other comprehensive gain, net of tax $ 1.8 $ 40.6 In the next twelve months , we estimate that $ 1.6 million of unrealized gains, net of tax, related to commodity price hedging will be reclassified from other comprehensive income into earnings. See the consolidated statement of comprehensive income and consolidated statement of shareholders’ equity for amounts recorded in other comprehensive income and for amounts reclassified from accumulated other comprehensive (loss) income into net income for each of the three years ended December 31, 2022. For the years ended December 31, 2022, 2021 and 2020, the following amounts were recognized in earnings related to copper swap contracts: Year Ended December 31, 2022 2021 2020 (Dollars in millions) (Loss) gain from contracts where hedge accounting was not $ ( 6.5 ) $ ( 3.8 ) $ 9.2 The fair value associated with forward contracts related to foreign currency that are not designated as hedges are immediately charged to earnings. These amounts are classified in cost of sales in the consolidated statement of operations. As of December 31, 2022 and 2021, the fair value of outstanding foreign currency forward contracts is recorded in the balance sheet as follows: December 31, 2022 2021 (Dollars in millions) Derivative contracts $ 0.1 $ 0.1 Accrued liabilities ( 0.1 ) ( 0.5 ) Net (liability) on balance sheet $ 0.0 $ ( 0.3 ) As of December 31, 2022 and 2021, the net currency units outstanding were: December 31, 2022 2021 (In millions) New Zealand Dollars NZD 3.3 NZD 0.0 United States Dollars USD 9.3 USD 21.4

Common Stock and Senior Convert

Common Stock and Senior Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Common Stock And Senior Convertible Preferred Stock	18. Common Stock and Senior Convertible Preferred Stock Changes in senior convertible preferred stock, common stock and treasury stock for the three years ended December 31, 2022 are as follows: December 31, 2022 2021 2020 (Shares in thousands) Senior Convertible Preferred Stock: Balance at beginning and end of year 0 0 0 Common Stock: Balance at beginning of year 24,027 23,688 23,321 Issued for employee stock plans 520 339 367 Balance at end of year 24,547 24,027 23,688 Treasury Stock: Balance at beginning of year ( 2,931 ) ( 2,590 ) ( 2,516 ) Shares repurchased ( 853 ) ( 341 ) ( 74 ) Balance at end of year ( 3,784 ) ( 2,931 ) ( 2,590 )

Commitments and Contingent Liab

Commitments and Contingent Liabilities	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities	19. 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 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 December 31, 2022 , compared to 59 plaintiffs in 31 cases pending as of December 31, 2021. As of December 31, 2022 , 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, Dow Chemical Company, 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 no t 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 “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 are approximately $ 1.1 billion and $ 1.7 billion, respectively. These costs may increase given the remedy will not be implemented for several years. Responsibility for implementing and funding that work will be decided in the 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 to 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 notifying it 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 $ 4.1 million as of December 31, 2022. 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 December 31, 2022 , our estimated environmental remediation liability for these sites totals $ 3.9 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 December 31, 2022 , our estimated environmental remediation liability for the acquired site totals $ 1.3 million. Environmental Reserves Rollforward . The following table reflects changes in the accrual for environmental remediation. A total of $ 2.5 million and $ 2.8 million are classified as current liabilities as of December 31, 2022 and December 31, 2021, respectively: December 31, 2022 2021 (Dollars in millions) Balance at beginning of year $ 10.7 $ 11.0 Expense 1.6 0.3 Revision of reserves 0.0 ( 0.1 ) Cash expenditures ( 1.1 ) ( 0.4 ) Currency translation ( 0.3 ) ( 0.1 ) Balance at end of year $ 10.9 $ 10.7

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2022
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS For the years ended December 31, 2022, 2021 and 2020 Balance at Increase Balance Beginning (Decrease) Net Currency at End of Year to Expense Write-offs Translation of Year (Dollars in millions) 2022 Allowance for doubtful accounts $ 3.3 $ 0.3 $ ( 0.1 ) $ 0.0 $ 3.5 Deferred tax valuation allowance $ 44.5 $ 0.9 $ ( 0.9 ) $ ( 0.7 ) $ 43.8 2021 Allowance for doubtful accounts $ 2.6 $ 1.2 $ ( 0.5 ) $ 0.0 $ 3.3 Deferred tax valuation allowance $ 44.6 $ 3.6 $ ( 3.6 ) $ ( 0.1 ) $ 44.5 2020 Allowance for doubtful accounts $ 2.6 $ 0.2 $ ( 0.2 ) $ 0.0 $ 2.6 Deferred tax valuation allowance $ 58.0 $ ( 12.1 ) $ ( 1.7 ) $ 0.4 $ 44.6

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of presentation – The consolidated financial statements include our accounts and all majority-owned subsidiaries for which we are deemed to exercise control over its operations. All significant intercompany transactions have been eliminated in consolidation. Certain prior period amounts in the Notes to Consolidated Financial Statements have been reclassified to conform to the current period’s presentation.
Use of Estimates	Use of estimates – Accounting principles generally accepted in the United States require management to make estimates and judgments that affect the reported amounts of assets and liabilities and the disclosure of contingencies on the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Estimates have been prepared on the basis of the most current and best available information and actual results could differ materially from these estimates.
Revenue Recognition	Revenue recognition – Revenue is recognized upon the completion of performance obligations under our contracts with customers and when control of a good or service is transferred to the customer. Substantially all of our contracts with customers are ship and invoice arrangements where revenue is recognized when we complete our performance obligations and transfer control to the customer. Revenue recognition generally occurs at the point of shipment; however in certain circumstances as shipping terms dictate, we transfer control and revenue is recognized at the point of destination. Payment terms are typically within 45 days. Shipping and handling costs are included as a component of cost of sales. We recognize revenue related to the procurement of certain untreated railroad crossties upon delivery to our plant and acceptance by the customer. Service revenue, consisting primarily of wood treating services, is recognized at the time the service is provided and the performance obligation is satisfied. Payment on sales of untreated railroad crossties and wood treating services are generally due within 30 days of the invoice date.
Contract Balances	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 consolidated balance sheet. Contract assets of $ 8.3 million and $ 7.9 million are recorded within accounts receivable, net of allowance within the consolidated balance sheet as of December 31, 2022 and December 31, 2021 , respectively.
Cash and Cash Equivalents	Cash and cash equivalents - Cash and cash equivalents include cash on hand and on deposit and investments with an original maturity of 90 days or less.
Accounts Receivable	Accounts receivable – We maintain allowances for doubtful accounts for estimated losses resulting from the inability of customers to make required payments. In circumstances where we become aware of a specific customer’s inability to meet its financial obligations to Koppers, a specific reserve for bad debts is recorded against amounts due. If the financial condition of our customers were to deteriorate, resulting in an inability to make payments, additional allowances may be required.
Inventories	Inventories – In the United States, CMC and RUPS inventories are valued at the lower of cost, utilizing the last-in, first-out (“LIFO”) basis, or net realizable value. Utilities and industrial products inventories are valued at the lower of cost, utilizing the moving average cost basis, or net realizable value. PC inventories and all other inventories outside of the United States are valued at the lower of cost, utilizing the first-in, first-out (“FIFO”) basis, and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. LIFO inventories constituted approximately 52 percent and 45 percent of the FIFO inventory value at December 31, 2022 and 2021, respectively. In 2022, 2021 and 2020 , we recorded inventory write-downs of $ 1.2 million, $ 0.6 million and $0 .6 million, respectively, related to lower of cost and net realizable value for our subsidiaries that value inventory on the FIFO basis.
Property, Plant and Equipment	Property, plant and equipment – Property, plant and equipment are recorded at purchased cost and include improvements which significantly increase capacities or extend useful lives of existing plant and equipment. Depreciation expense is calculated by applying the straight-line method over estimated useful lives. Estimated useful lives for buildings generally range from ten to 20 years and depreciable lives for machinery and equipment generally range from three to 15 years . Net gains and losses related to asset disposals are recognized in earnings in the period in which the disposal occurs. Routine repairs, replacements and maintenance are expensed as incurred. We periodically evaluate whether current facts and circumstances indicate that the carrying value of depreciable long-lived assets may not be recoverable. If an asset, or logical grouping of assets, is determined to be impaired, the asset is written down to its fair value using discounted future cash flows and, if available, quoted market prices. Refer to Note 4 – “Plant Closures and Divestitures” for additional information.
Goodwill and Other Intangible Assets	Goodwill and other intangible assets – Goodwill and other purchased intangible assets are included in the identifiable assets of the business segment to which they have been assigned. Goodwill is not amortized and is subject to an impairment test that we conduct annually or more frequently if a change in circumstances or the occurrence of events indicates that potential impairment exists. We perform an assessment of goodwill at the reporting unit level, utilizing a combination of an income approach, using a discounted cash flow methodology, and a market approach, by comparing the estimated fair value calculations of each reporting unit with its net book value. The discounted cash flow calculations are dependent on several subjective factors including the timing of future forecasted cash flows including future forecasted revenue growth rates, and the discount rate. If assumptions or estimates in the fair value calculations change or if future forecasted cash flows or future forecasted growth rates vary from what was planned, this may impact the impairment analysis. We performed an impairment test for goodwill for each of the reporting units using the above quantitative testing approach. Based on the evaluations performed, we determined that the fair value of each of the reporting units exceeded its carrying amount, and therefore, we determined that goodwill was no t impaired. Identifiable intangible assets, other than goodwill, are recorded at fair value. Identifiable intangible assets are amortized on a straight-line basis over their estimated useful lives.
Deferred Income Taxes	Deferred income taxes – Deferred tax assets and liabilities are recognized for future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. The effect on deferred tax assets and liabilities of a change in tax laws is recognized in earnings in the period the new laws are enacted. A valuation allowance is recorded to reduce the carrying amounts of deferred tax assets unless it is more likely than not that such assets will be realized.
Leases	Leases – Lease arrangements are determined whether or not to be a lease at inception. Right-of-use (“ROU”) assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments. ROU lease liabilities are recognized based on the present value of the future minimum lease payments over the term of the lease as of the start date and may include consideration of certain adjustments including non-lease components. ROU assets are determined based on the determined ROU lease liability and may include the consideration of certain adjustments including initial direct costs, prepaid lease payments, lease incentives received, and non-lease components. The option to extend or terminate a lease is included in the determination of the ROU asset and lease liability only when it is reasonably certain that we will exercise that option.
Asset Retirement Obligations	Asset retirement obligations – Asset retirement obligations are initially recorded at present value and are capitalized as part of the cost of the related long-lived asset when sufficient information is available to estimate present value. The capitalized costs are subsequently charged to depreciation expense over the estimated useful life of the related long-lived asset. The present value of the obligation is determined by calculating the discounted value of expected future cash flows and accretion expense is recorded each month to ultimately increase this obligation to fair value. We recognize asset retirement obligations for the removal and disposal of residues; dismantling of certain tanks required by governmental authorities; cleaning and dismantling costs for owned rail cars; cleaning costs for leased rail cars and barges; and site demolition, when required by governmental authorities or by contract. The following table describes changes to our asset retirement obligation liabilities: December 31, 2022 2021 (Dollars in millions) Asset retirement obligation at beginning of year $ 13.2 $ 19.8 Accretion expense 1.0 1.0 Revision in estimated cash flows 2.2 ( 0.3 ) Cash expenditures ( 1.0 ) ( 7.3 ) Balance at end of year $ 15.5 $ 13.2
Litigation and Contingencies	Litigation and contingencies – Amounts associated with litigation and contingencies are accrued when management, after taking into consideration the facts and circumstances of each matter including any settlement offers, has determined that it is probable that a liability has been incurred and the amount of loss can be reasonably estimated. Legal costs for litigation are expensed as incurred with the exception of legal fees relating to the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, as amended (“CERCLA”), sites.
Environmental Liabilities	Environmental liabilities – We accrue for remediation costs and penalties when the responsibility to remediate is probable and the amount of related cost is reasonably estimable. If only a range of potential liability can be estimated and no amount within the range is more probable than another, the accrual is recorded at the low end of that range. Remediation liabilities are discounted if the amount and timing of the cash disbursements are readily determinable.
New Accounting Pronouncements	New Accounting Pronouncements In March 2022, the Financial Accounting Standards Board ("FASB") issued ASU No. 2022-01, "Derivatives and Hedging (Topic 815): Fair Value Hedging —Portfolio Layer Method." This ASU amends and simplifies existing guidance in order to allow companies to more accurately present the economic effects of risk management activities in financial statements. ASU No. 2022-01 is effective for periods beginning after December 15, 2022, and earlier adoption is permitted. The adoption of this ASU will not have a material impact on our financial statements as we principally utilize cash flow hedges.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Summary of Asset Retirement Obligation Liabilities	The following table describes changes to our asset retirement obligation liabilities: December 31, 2022 2021 (Dollars in millions) Asset retirement obligation at beginning of year $ 13.2 $ 19.8 Accretion expense 1.0 1.0 Revision in estimated cash flows 2.2 ( 0.3 ) Cash expenditures ( 1.0 ) ( 7.3 ) Balance at end of year $ 15.5 $ 13.2

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2022
Business Combination and Asset Acquisition [Abstract]
Schedule of Fair Value of Assets and Liabilities Acquired	The fair value of assets and liabilities acquired is set forth in the following table: (Dollars in millions) Accounts receivable $ 4.3 Inventory 7.4 Property, plant and equipment 4.5 Total assets acquired 16.2 Accounts payable and accrued liabilities 0.7 Net assets acquired $ 15.5

Discontinued Operations (Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2022
Discontinued Operations and Disposal Groups [Abstract]
Schedule of Net Sales and Operating Loss from Discontinued Operations	Net sales and operating loss from discontinued operations for the year ended December 31, 2020 consist of the following amounts: Year Ended December 31, 2020 (Dollars in millions) Net sales $ 31.6 Operating loss ( 5.0 )
Schedule of Net cash Inflows and Outflows From Discontinued Operations	The cash flows related to KJCC have not been restated in the Consolidated Statement of Cash Flows. Net cash inflows and outflows from discontinued operations for the year ended December 31, 2020 consist of the following amounts: Year Ended December 31, 2020 (Dollars in millions) Net cash provided by operating activities $ 0.7 Net cash used in investing activities ( 0.9 ) Effect of exchange rate changes on cash ( 0.5 ) Net decrease in cash and cash equivalents ( 0.7 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Schedule of Company's Financial Instruments	Carrying amounts and the related estimated fair values of our financial instruments as of December 31, 2022 are as follows: December 31, 2022 December 31, 2021 Fair Value Carrying Fair Value Carrying (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) $ 801.1 $ 825.3 $ 804.1 $ 789.1

Earnings and Dividends per Co_2

Earnings and Dividends per Common Share (Tables)	12 Months Ended
	Dec. 31, 2022
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: Year Ended December 31, 2022 2021 2020 (Dollars in millions, except share amounts, in thousands, and per share amounts) Net income attributable to Koppers $ 63.4 $ 85.2 $ 122.0 (Loss) gain on sale of discontinued operations, net of tax 0.0 , $ 0.1 and $( 7.4 ) ( 0.6 ) ( 0.2 ) 31.9 Income from continuing operations attributable to Koppers $ 64.0 $ 85.4 $ 90.1 Weighted average common shares outstanding: Basic 20,977 21,238 20,992 Effect of dilutive securities 336 687 382 Diluted 21,313 21,925 21,374 Earnings per common share – continuing operations: Basic earnings per common share $ 3.05 $ 4.02 $ 4.25 Diluted earnings per common share 3.00 3.90 4.17 Other data: Antidilutive securities excluded from computation of diluted 952 436 717

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2022
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 stock options on the date of grant using the Black-Scholes-Merton model and the assumptions listed below: January 2022 Grant January 2021 Grant March 2020 Grant March 2019 Grant Grant date price per share of stock $ 32.19 $ 29.84 $ 19.63 $ 26.63 Expected dividend yield per share 0.00 % 0.00 % 0.00 % 0.00 % Expected life in years 6.76 6.64 6.40 6.14 Expected volatility 54.50 % 54.80 % 42.85 % 39.44 % Risk-free interest rate 1.52 % 0.59 % 0.87 % 2.53 % Grant date fair value per share of stock $ 17.58 $ 15.79 $ 8.42 $ 11.29
Summary of Performance Stock Units	The following table shows a summary of the performance stock units as of December 31, 2022: Performance Period Minimum Target Maximum 2021 – 2023 67,516 115,972 164,505 2022 – 2024 18,111 120,039 220,851
Summary of Status and Activity of Non-Vested Stock Awards	The following table shows a summary of the status and activity of non-vested stock awards for the year ended December 31, 2022: Restricted Performance Total Weighted Average Non-vested at January 1, 2022 505,905 474,166 980,071 $ 30.79 Granted 250,760 153,236 403,996 $ 35.78 Performance share adjustment 0 ( 124,932 ) ( 124,932 ) $ 25.24 Vested ( 202,716 ) ( 256,956 ) ( 459,672 ) $ 34.33 Forfeited ( 29,337 ) ( 9,501 ) ( 38,838 ) $ 27.93 Non-vested at December 31, 2022 524,612 236,013 760,625 $ 32.36
Summary of Status and Activity of Stock Options	The following table shows a summary of the status and activity of stock options for the year ended December 31, 2022: Options Weighted Average Weighted Average Aggregate Intrinsic Outstanding at December 31, 2021 1,054,166 $ 26.89 Granted 98,108 $ 32.19 Expired ( 30,138 ) $ 38.21 Outstanding at December 31, 2022 1,122,136 $ 27.05 4.61 $ 5.5 Exercisable at December 31, 2022 843,475 $ 26.99 3.52 $ 4.7
Schedule of Stock-based Compensation Expense Recognized	Total stock-based compensation expense recognized under our LTIP and employee stock purchase plan for the three years ended December 31, 2022 is as follows: Year Ended December 31, 2022 2021 2020 (Dollars in millions) Stock-based compensation expense recognized: Selling, general and administrative expenses $ 13.2 $ 13.0 $ 11.3 Less related income tax benefit 4.4 3.7 2.2 Decrease in net income attributable to Koppers $ 8.8 $ 9.3 $ 9.1 Intrinsic value of exercised stock options $ 0.0 $ 2.2 $ 0.0 Cash received from the exercise of stock options $ 0.0 $ 2.3 $ 0.0
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 unit awards on the date of the grant using assumptions listed below: January 2022 Grant January 2021 Grant March 2020 Grant Grant date price per share of stock $ 32.19 $ 29.84 $ 19.63 Expected dividend yield per share 0.00 % 0.00 % 0.00 % Expected volatility 66.90 % 68.70 % 45.60 % Risk-free interest rate 1.10 % 0.16 % 0.72 % Look-back period in years 3.00 3.00 2.83 Grant date fair value per share of stock $ 45.19 $ 41.50 $ 11.56

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2022
Segment Reporting [Abstract]
Summary of Results of Segment Operations	The following table sets forth certain sales and operating data by segment for the periods indicated: Year Ended December 31, 2022 2021 2020 (Dollars in millions) Revenues from external customers: Railroad and Utility Products and Services $ 788.3 $ 729.9 $ 759.1 Performance Chemicals 579.9 503.3 526.3 Carbon Materials and Chemicals (a) 612.3 445.4 383.7 Total $ 1,980.5 $ 1,678.6 $ 1,669.1 Intersegment revenues: Performance Chemicals $ 22.2 $ 15.9 $ 13.7 Carbon Materials and Chemicals 74.3 75.3 78.7 Total $ 96.5 $ 91.2 $ 92.4 Depreciation and amortization expense: Railroad and Utility Products and Services $ 22.3 $ 22.3 $ 20.1 Performance Chemicals 15.3 17.9 18.1 Carbon Materials and Chemicals (b) 18.5 17.5 15.9 Total $ 56.1 $ 57.7 $ 54.1 Adjusted EBITDA: Railroad and Utility Products and Services $ 53.6 $ 45.4 $ 65.3 Performance Chemicals 75.5 101.8 100.7 Carbon Materials and Chemicals 99.0 76.3 45.0 Items excluded from the determination of segment Impairment, restructuring and plant closure ( 1.1 ) ( 4.2 ) ( 15.7 ) Gain on sale of assets 2.5 31.2 0.0 LIFO (expense) benefit ( 25.6 ) ( 28.2 ) 13.7 Mark-to-market commodity hedging (losses) gains ( 6.5 ) ( 3.8 ) 9.2 Inventory adjustment (c) ( 1.1 ) 0.0 0.0 Pension settlement 0.0 0.0 ( 0.1 ) Discretionary incentive (d) 0.0 0.0 ( 3.0 ) Interest expense ( 44.8 ) ( 40.5 ) ( 48.9 ) Depreciation and amortization ( 56.1 ) ( 57.7 ) ( 54.1 ) Depreciation in impairment and restructuring charges 0.0 ( 0.7 ) ( 2.0 ) Income tax provision ( 31.6 ) ( 34.5 ) ( 21.0 ) Discontinued operations ( 0.6 ) ( 0.2 ) 31.9 Net income $ 63.2 $ 84.9 $ 121.0 Capital expenditures: Railroad and Utility Products and Services $ 47.2 $ 62.0 $ 31.3 Performance Chemicals 10.6 17.7 12.1 Carbon Materials and Chemicals (e) 45.7 42.9 24.8 Corporate 1.8 2.4 1.6 Total $ 105.3 $ 125.0 $ 69.8 (a) Revenue excludes KJCC discontinued operations of $ 31.6 million for the year ended December 31, 2020. (b) Depreciation and amortization expense excludes KJCC discontinued operations of $ 0.6 million for the year ended December 31, 2020. (c) Represents fair value step-up on inventory acquired in a business acquisition as described in Note 3 – "Acquisitions". (d) Represents a one-time employee incentive associated with the sale of KJCC as described in Note 5 – "Discontinued Operations". (e) Capital expenditures includes KJCC discontinued operations of $ 0.6 million for the year ended December 31, 2020.
Summary of Tangible and Intangible Assets by Segments	The following table sets forth tangible and intangible assets allocated to each of our segments as of the dates indicated: December 31, 2022 2021 (Dollars in millions) Segment assets: Railroad and Utility Products and Services $ 660.8 $ 594.1 Performance Chemicals 516.9 586.9 Carbon Materials and Chemicals 500.5 447.1 Segment assets 1,678.2 1,628.1 Prepaid insurance and other assets 16.0 16.5 Property, plant and equipment, net 6.8 6.6 Operating lease right-of-use assets 10.4 10.7 Total $ 1,711.4 $ 1,661.9 Goodwill: Railroad and Utility Products and Services $ 120.6 $ 120.9 Performance Chemicals 173.4 175.1 Total $ 294.0 $ 296.0
Schedule of Revenues and Long-Lived Assets by Geographic Area	Revenues and Long-lived Assets by Geographic Area Year Revenue Long-lived (Dollars in millions) United States 2022 $ 1,271.1 $ 902.9 2021 1,134.2 857.3 2020 1,170.1 832.0 Australasia 2022 283.0 73.8 2021 230.6 78.9 2020 194.3 82.0 Europe 2022 248.9 67.6 2021 195.8 63.3 2020 162.3 83.2 Other countries 2022 177.5 18.6 2021 118.0 19.3 2020 142.4 18.5 Total (a) 2022 $ 1,980.5 $ 1,062.9 2021 $ 1,678.6 $ 1,018.8 2020 $ 1,669.1 $ 1,015.7 (a) Revenue excludes KJCC discontinued operations of $ 31.6 million for the year ended December 31, 2020.
Schedule of Segment Revenues for Significant Product Lines	Segment Revenues for Significant Product Lines Year Ended December 31, 2022 2021 2020 (Dollars in millions) Railroad and Utility Products and Services: Railroad treated products $ 457.4 $ 414.4 $ 405.1 Utility poles 227.9 228.0 241.7 Railroad infrastructure services 61.8 56.0 63.5 Rail joints 28.0 22.7 20.3 Other products 13.2 8.8 28.6 788.3 729.9 759.1 Performance Chemicals: Wood preservative products 561.2 489.1 510.7 Other products 18.7 14.2 15.6 579.9 503.3 526.3 Carbon Materials and Chemicals: Pitch and related products 390.7 260.3 230.9 Phthalic anhydride and other chemicals 109.1 75.6 66.4 Creosote and distillates 62.9 52.1 40.0 Naphthalene 36.0 27.1 19.7 Other products 13.6 30.3 26.7 612.3 445.4 383.7 Total (a) $ 1,980.5 $ 1,678.6 $ 1,669.1 (a) Revenue excludes KJCC discontinued operations of $ 31.6 million for the year ended December 31, 2020.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Summary of Income Tax Provision	Components of our income tax provision are as follows: Year Ended December 31, 2022 2021 2020 (Dollars in millions) Current: Federal $ 0.0 $ ( 1.5 ) $ 0.8 State 0.6 0.9 0.7 Foreign 28.4 18.2 11.1 Total current tax provision 29.0 17.6 12.6 Deferred: Federal 0.2 10.6 6.1 State ( 0.6 ) 1.1 1.6 Foreign 3.0 5.2 0.7 Total deferred tax provision 2.6 16.9 8.4 Total income tax provision $ 31.6 $ 34.5 $ 21.0
Summary of Income Taxes Reconciled with Federal Statutory Rate	The provision for income taxes is reconciled with the federal statutory income tax rate as follows: Year Ended December 31, 2022 2021 2020 Federal income tax rate 21.0 % 21.0 % 21.0 % Foreign earnings taxed at different rates 8.7 4.3 2.9 GILTI inclusion, net of foreign tax credits 1.7 0.2 4.0 Valuation allowance adjustments 0.9 1.9 ( 12.1 ) Deferred tax adjustments 0.0 ( 0.2 ) ( 2.2 ) Change in tax contingency reserves ( 0.1 ) ( 1.1 ) ( 0.2 ) State income taxes, net of federal tax benefit ( 0.2 ) 2.1 2.2 Other 1.1 0.6 3.5 33.1 % 28.8 % 19.1 %
Summary of Deferred Tax Assets and Liabilities	Significant components of our deferred tax assets and liabilities are as follows: Year Ended December 31, 2022 2021 (Dollars in millions) Deferred tax assets: Federal and state tax loss carryforwards, expiring in 2023 to 2042 $ 22.6 $ 24.4 Tax credits 17.4 17.5 Reserves, including insurance and environmental 9.3 9.0 Pension and other post-retirement benefits obligations 8.2 9.6 Foreign tax loss carryforwards 6.6 7.4 Accrued employee compensation 6.5 7.1 Interest disallowance 6.4 0.0 Asset retirement obligations 5.3 4.5 Inventory 4.6 5.9 Other 4.6 3.3 Valuation allowance ( 43.8 ) ( 44.5 ) Total deferred tax assets 47.7 44.2 Deferred tax liabilities: Tax over book depreciation and amortization 52.3 44.0 Gain on derivative contracts 0.7 14.3 Other 4.5 4.3 Total deferred tax liabilities 57.5 62.6 Net deferred tax liabilities $ ( 9.8 ) $ ( 18.4 )
Summary of Valuation Allowances Recorded to Offset Deferred Tax Assets	A valuation allowance is necessary when it is more likely than not that a deferred tax asset will not be realized. Certain deferred tax assets reflected above are not expected to be realized and a valuation allowance has been provided for them. Valuation allowances are recorded to offset the following deferred tax assets: December 31, 2022 2021 State temporary differences, net operating losses and tax credits $ 19.4 $ 19.2 Federal foreign tax credits 16.1 16.1 Foreign temporary differences, net operating losses and capital losses 8.3 9.1 Federal temporary differences 0.0 0.1 Total valuation allowances $ 43.8 $ 44.5
Summary of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: December 31, 2022 2021 2020 (Dollars in millions) Balance at beginning of year $ 1.5 $ 2.5 $ 2.1 Additions based on tax provisions related to the current year 0.1 0.1 0.2 Additions for tax provisions of prior years 0.0 0.0 0.5 Reductions resulting from a lapse in the statute of limitations ( 0.2 ) ( 1.1 ) ( 0.3 ) Balance at end of year $ 1.4 $ 1.5 $ 2.5

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2022
Inventory Disclosure [Abstract]
Components of Inventories	Inventories as of December 31, 2022 and December 31, 2021 were as follows: December 31, 2022 2021 (Dollars in millions) Raw materials $ 318.5 $ 266.8 Work in process 10.2 12.6 Finished goods 130.4 112.1 459.1 391.5 Less revaluation to LIFO 103.4 77.7 Inventories, net $ 355.7 $ 313.8

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, plant and equipment as of December 31, 2022 and December 31, 2021 were as follows: December 31, 2022 2021 (Dollars in millions) Land $ 15.0 $ 15.2 Buildings 80.3 75.8 Machinery and equipment 924.1 836.8 1,019.4 $ 927.8 Less accumulated depreciation 462.1 438.7 Property, plant and equipment, net $ 557.3 $ 489.1

Goodwill and Other Identifiab_2

Goodwill and Other Identifiable Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in Carrying Amount of Goodwill	The change in the carrying amount of goodwill attributable to each reporting unit for the years ended December 31, 2022 and December 31, 2021 was as follows: Performance Chemicals Railroad Products and Services Utility Total (Dollars in millions) Balance at December 31, 2020 $ 176.7 $ 41.1 $ 80.0 $ 297.8 Currency translation ( 1.6 ) 0.0 ( 0.2 ) ( 1.8 ) Balance at December 31, 2021 $ 175.1 $ 41.1 $ 79.8 $ 296.0 Currency translation ( 1.7 ) ( 0.1 ) ( 0.2 ) ( 2.0 ) Balance at December 31, 2022 $ 173.4 $ 41.0 $ 79.6 $ 294.0
Schedule of Identifiable Intangible Assets	Our identifiable intangible assets are being amortized over their estimated useful lives and are summarized below: December 31, 2022 2021 Estimated Weighted Gross Accumulated Net Gross Accumulated Net (Dollars in millions) Customer contracts 9 to 18 9.0 $ 224.9 $ 110.5 $ 114.4 $ 226.9 $ 97.6 $ 129.3 Technology 4 to 12 3.6 26.4 26.0 0.4 26.5 25.9 0.6 Trademarks 2 to 18 11.0 7.7 6.5 1.2 7.6 6.4 1.2 Supply contracts 10 0.0 2.4 2.4 0.0 2.4 2.4 0.0 Non-compete 12 1.8 1.6 1.5 0.1 1.7 1.3 0.4 Total 8.9 $ 263.0 $ 146.9 $ 116.1 $ 265.1 $ 133.6 $ 131.5
Schedule of Future Amortization Expense	Estimated amortization expense for the next five years is summarized below: Estimated (Dollars in millions) 2023 $ 14.4 2024 14.2 2025 13.7 2026 12.4 2027 12.0

Pensions and Post-Retirement _2

Pensions and Post-Retirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans	Net periodic pension costs for 2022, 2021 and 2020 were as follows: Year Ended December 31, Pension Benefits Other Benefits 2022 2021 2020 2022 2021 2020 (Dollars in millions) Service cost $ 1.2 $ 1.5 $ 1.4 $ 0.0 $ 0.1 $ 0.1 Interest cost 5.6 5.2 6.4 0.3 0.3 0.3 Expected return on plan assets ( 7.7 ) ( 7.4 ) ( 7.9 ) 0.0 0.0 0.0 Amortization of net loss (gain) 1.8 1.4 1.7 ( 0.1 ) 0.0 ( 0.2 ) Settlements and curtailments 0.0 0.0 0.1 0.0 0.0 0.0 Net periodic benefit cost $ 0.9 $ 0.7 $ 1.7 $ 0.2 $ 0.4 $ 0.2
Schedule of Change in Funded Status of Pension and Post-Retirement Plans	The change in the funded status of the pension and post-retirement plans as of December 31, 2022 and December 31, 2021 is as follows: Year Ended December 31, Pension Benefits Other Benefits 2022 2021 2022 2021 (Dollars in millions) Change in benefit obligation: Benefit obligation at beginning of year $ 219.6 $ 233.3 $ 9.8 $ 10.5 Service cost 1.2 1.5 0.0 0.1 Interest cost 5.6 5.2 0.3 0.3 Actuarial gains ( 51.8 ) ( 9.0 ) ( 3.4 ) ( 0.6 ) Settlements ( 1.0 ) 0.0 0.0 0.0 Currency translation ( 5.8 ) ( 0.6 ) 0.0 0.0 Benefits paid ( 10.8 ) ( 10.8 ) ( 0.7 ) ( 0.5 ) Benefit obligation at end of year 157.0 219.6 6.0 9.8 Change in plan assets: Fair value of plan assets at beginning of year 190.0 208.0 0.0 0.0 Actual return on plan assets ( 46.1 ) ( 8.9 ) 0.0 0.0 Employer contribution 0.9 2.3 0.7 0.5 Settlements ( 1.0 ) 0.0 0.0 0.0 Currency translation ( 5.6 ) ( 0.6 ) 0.0 0.0 Benefits paid ( 10.8 ) ( 10.8 ) ( 0.7 ) ( 0.5 ) Fair value of plan assets at end of year 127.4 190.0 0.0 0.0 Funded status of the plan $ ( 29.6 ) $ ( 29.6 ) $ ( 6.0 ) $ ( 9.8 ) Plan Data Year Ended December 31, Pension Benefits Other Benefits 2022 2021 2022 2021 (Dollars in millions) Amounts recognized in the balance sheet Noncurrent assets $ 0.6 $ 0.8 $ 0.0 $ 0.0 Current liabilities 1.0 1.0 0.5 0.6 Noncurrent liabilities 29.2 29.4 5.5 9.2 Pension plans with projected benefit obligations Benefit obligation $ 154.4 $ 215.7 Fair value of plan assets 124.2 185.3 Pension plans with accumulated benefit Accumulated benefit obligation $ 154.2 $ 215.5 Fair value of plan assets 124.2 185.3
Schedule of Projected Benefit Payments	Benefit payments for pension benefits, which are primarily funded by the pension plan assets, and other benefits, which are funded by general corporate assets, are expected to be paid as follows: Pension Benefits Other Benefits (Dollars in millions) 2023 $ 11.6 $ 0.5 2024 11.3 0.5 2025 11.8 0.5 2026 11.3 0.5 2027 11.2 0.5 Next five years 57.9 2.4
Schedule of Weighted-Average Assumptions	Weighted-Average Assumptions December 31, Pension Benefits Other Benefits 2022 2021 2022 2021 Discount rate 5.42 % 2.67 % 5.58 % 2.97 % Expected return on plan assets 4.65 3.91 Rate of compensation increase 3.13 3.00 Initial medical trend rate 5.40 5.40
Schedule of Weighted Average Asset Allocation for Company's Pension Plans	The weighted average asset allocation for our pension plans as of December 31 by asset category is as follows: December 31, 2022 2021 Debt securities 52 % 49 % Equity securities 20 21 Other 28 30 100 % 100 %
Schedule of Pension Plan Assets at Fair Value	The following tables set forth by level, our pension plan assets at fair value, within the fair value hierarchy, as of December 31, 2022 and December 31, 2021: December 31, 2022 Quoted prices in Significant Significant Total (Dollars in millions) U.S. equity securities $ 0.0 $ 4.9 $ 0.0 $ 4.9 International equity securities 0.0 11.1 0.0 11.1 U.S. debt securities 0.0 39.2 0.0 39.2 International debt securities 0.0 2.6 0.0 2.6 Insurance annuity contract and other 0.0 0.5 31.5 32.0 Cash and cash equivalents 0.0 1.6 0.0 1.6 $ 0.0 $ 59.9 $ 31.5 $ 91.4 Investments measured at NAV (a) 36.0 Total assets at fair value $ 127.4 (a) The fair value amounts presented in the table above are intended to permit reconciliations of the fair value hierarchy to the total plan assets. December 31, 2021 Quoted prices in Significant Significant Total (Dollars in millions) U.S. equity securities $ 0.0 $ 7.9 $ 0.0 $ 7.9 International equity securities 0.0 17.9 0.0 17.9 U.S. debt securities 0.0 64.9 0.0 64.9 International debt securities 0.0 3.6 0.0 3.6 Other investments 0.0 0.6 52.3 52.9 Cash and cash equivalents 0.0 2.1 0.0 2.1 $ 0.0 $ 97.0 $ 52.3 $ 149.3 Investments measured at NAV (a) 40.7 Total assets at fair value $ 190.0 (a) The fair value amounts presented in the table above are intended to permit reconciliations of the fair value hierarchy to the total plan assets.

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Schedule of Long-Term Debt Instruments	Debt as of December 31, 2022 and December 31, 2021 was as follows: December 31, Weighted Maturity 2022 2021 Term Loan - - $ 0.0 $ 2.0 Revolving Credit Facility - - 0.0 287.1 Revolving Credit Facility 6.72 % 2027 325.3 0.0 Senior Notes due 2025 6.00 % 2025 500.0 500.0 Total debt 825.3 789.1 Less short-term debt and current maturities of 0.0 2.0 Less unamortized debt issuance costs 7.6 5.6 Long-term debt $ 817.7 $ 781.5
Schedule of Debt Maturities	At December 31, 2022 the aggregate debt maturities for the next five years are as follows: (Dollars in millions) 2023 $ 0.0 2024 0.0 2025 500.0 2026 0.0 2027 325.3 Total debt $ 825.3

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Summary of Amount and Timing of Cash Flows From Operating Leases	The following table presents information about the amount and timing of cash flows arising from our operating leases as of December 31, 2022: (Dollars in millions) 2023 $ 26.2 2024 22.3 2025 17.1 2026 12.3 2027 10.0 Thereafter 20.6 Total lease payments $ 108.5 Less: Interest ( 21.7 ) Present value of lease liabilities $ 86.8
Schedule of Supplemental Consolidated Balance Sheet Information Related to Leases	Supplemental consolidated balance sheet information related to leases is as follows: December 31, 2022 2021 (Dollars in millions) Operating leases: Operating lease right-of-use assets $ 86.3 $ 91.2 Current operating lease liabilities $ 20.5 $ 21.3 Operating lease liabilities 66.3 70.3 Total operating lease liabilities $ 86.8 $ 91.6 Weighted average remaining lease term, in years 5.6 5.8 Weighted average discount rate 7.2 % 7.4 %

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Outstanding Copper Swap Contracts	As of December 31, 2022 and December 31, 2021, we had outstanding copper swap contracts of the following amounts: Units Outstanding (in Pounds) Net Fair Value - Asset December 31, December 31, 2022 2021 2022 2021 (Amounts in millions) Cash flow hedges 21.3 29.0 $ 2.5 $ 53.8 Not designated as hedges 6.0 6.1 0.6 7.1 Total 27.3 35.1 $ 3.1 $ 60.9
Schedule of Fair Value of Outstanding Copper Swap Contracts Recorded in Balance Sheet	As of December 31, 2022 and December 31, 2021, the fair value of the outstanding copper swap contracts is recorded in the balance sheet as follows: December 31, 2022 2021 (Dollars in millions) Derivative contracts $ 3.4 $ 60.9 Accrued liabilities ( 0.3 ) 0.0 Net asset on balance sheet $ 3.1 $ 60.9 Accumulated other comprehensive gain, net of tax $ 1.8 $ 40.6
Summary of Amount Recognized in Earnings Related to Copper Swap Contracts	For the years ended December 31, 2022, 2021 and 2020, the following amounts were recognized in earnings related to copper swap contracts: Year Ended December 31, 2022 2021 2020 (Dollars in millions) (Loss) gain from contracts where hedge accounting was not $ ( 6.5 ) $ ( 3.8 ) $ 9.2
Schedule of Fair Value of Outstanding Foreign Currency Forward Contracts	As of December 31, 2022 and 2021, the fair value of outstanding foreign currency forward contracts is recorded in the balance sheet as follows: December 31, 2022 2021 (Dollars in millions) Derivative contracts $ 0.1 $ 0.1 Accrued liabilities ( 0.1 ) ( 0.5 ) Net (liability) on balance sheet $ 0.0 $ ( 0.3 )
Summary of Net Currency Units Outstanding	As of December 31, 2022 and 2021, the net currency units outstanding were: December 31, 2022 2021 (In millions) New Zealand Dollars NZD 3.3 NZD 0.0 United States Dollars USD 9.3 USD 21.4

Common Stock and Senior Conve_2

Common Stock and Senior Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Schedule of Changes in Senior Convertible Preferred Stock, Common Stock and Treasury Stock	Changes in senior convertible preferred stock, common stock and treasury stock for the three years ended December 31, 2022 are as follows: December 31, 2022 2021 2020 (Shares in thousands) Senior Convertible Preferred Stock: Balance at beginning and end of year 0 0 0 Common Stock: Balance at beginning of year 24,027 23,688 23,321 Issued for employee stock plans 520 339 367 Balance at end of year 24,547 24,027 23,688 Treasury Stock: Balance at beginning of year ( 2,931 ) ( 2,590 ) ( 2,516 ) Shares repurchased ( 853 ) ( 341 ) ( 74 ) Balance at end of year ( 3,784 ) ( 2,931 ) ( 2,590 )

Commitments and Contingent Li_2

Commitments and Contingent Liabilities (Tables)	12 Months Ended
	Dec. 31, 2022
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 $ 2.5 million and $ 2.8 million are classified as current liabilities as of December 31, 2022 and December 31, 2021, respectively: December 31, 2022 2021 (Dollars in millions) Balance at beginning of year $ 10.7 $ 11.0 Expense 1.6 0.3 Revision of reserves 0.0 ( 0.1 ) Cash expenditures ( 1.1 ) ( 0.4 ) Currency translation ( 0.3 ) ( 0.1 ) Balance at end of year $ 10.9 $ 10.7

Description of Business - Addit

Description of Business - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2022 Segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	3

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Summary Of Significant Accounting Policies [Line Items]
Period for payment terms on ship and invoice arrangements.	45 days
Period for payment of approval basis sale	30 days
Contract Assets	$ 8,300,000	$ 7,900,000
Percentage of LIFO inventory	52%	45%
Inventory write-down	$ 1,200,000	$ 600,000	$ 600,000
Goodwill impairment charge	$ 0	$ 0	$ 0
Buildings [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	10 years
Buildings [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	20 years
Machinery and Equipment [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	3 years
Machinery and Equipment [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	15 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Asset Retirement Obligation Liabilities (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Asset Retirement Obligation Disclosure [Abstract]
Asset retirement obligation at beginning of year	$ 13.2	$ 19.8
Accretion expense	1	1
Revision in estimated cash flows (a)	2.2	(0.3)
Cash expenditures	(1)	(7.3)
Balance at end of period	$ 15.5	$ 13.2

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) $ in Millions	Oct. 31, 2022 USD ($)
Gross & Janes Co [Member]
Business Acquisition [Line Items]
Value of the assets acquired	$ 15.5

Acquisitions - Schedule of Fair

Acquisitions - Schedule of Fair Value of Assets and Liabilities Acquired (Detail) - Gross & Janes Co [Member] $ in Millions	Oct. 31, 2022 USD ($)
Business Acquisition [Line Items]
Accounts receivable	$ 4.3
Inventory	7.4
Property, plant and equipment	4.5
Total assets acquired	16.2
Accounts payable and accrued liabilities	0.7
Net assets acquired	$ 15.5

Plant Closure and Divestitures

Plant Closure and Divestitures - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended			3 Months Ended	12 Months Ended
	Mar. 31, 2022	Oct. 31, 2021	Feb. 28, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Restructuring Cost And Reserve [Line Items]
Gain on sale					$ 2.5	$ 31.2	$ 0
Railroad and Utility Products and Services [Member] | Facility [Member]
Restructuring Cost And Reserve [Line Items]
Gain on sale		$ 23.4
West Virginia [Member] | Coal Tar Distillation [Member]
Restructuring Cost And Reserve [Line Items]
Gain on sale			$ 5.7
Cash proceed from sale			$ 2.6
Pennsylvania [Member] | Coal Tar Distillation [Member]
Restructuring Cost And Reserve [Line Items]
Gain on sale				$ 1.8
Sweetwater, Tennessee [Member] | Railroad and Utility Products and Services [Member] | Pole Treating Facility [Member]
Restructuring Cost And Reserve [Line Items]
Gain on sale	$ 2.5

Discontinued Operations - Addit

Discontinued Operations - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Aug. 31, 2022	Sep. 30, 2020
Schedule Of Equity Method Investments [Line Items]
Restricted cash held with escrow					$ 1.5
Potential customary indemnity claims issued		$ 0.9
Potential customary indemnity claims shares issued		$ 0.7
Potential customary indemnity claims settled period		2022-04
Potential customary indemnity claims tax amount	$ 0.5
Discontinued operation, gain from disposal of discontinued operation, before income tax		$ 0	$ (0.3)	$ 35.8
Discontinued operation, gain on disposal of discontinued operation, net of tax		$ (0.6)	$ (0.2)	31.9
Koppers (Jiangsu) Carbon Chemical Company Limited [Member]
Schedule Of Equity Method Investments [Line Items]
Discontinued operation, gain from disposal of discontinued operation, before income tax				44.1
Discontinued operation, gain on disposal of discontinued operation, net of tax				$ 35.8
Koppers (Jiangsu) Carbon Chemical Company Limited [Member] | Carbon Materials and Chemicals [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage						75%

Discontinued Operations - Sched

Discontinued Operations - Schedule of Net Sales and Operating Loss from Discontinued Operations (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Discontinued Operations and Disposal Groups [Abstract]
Net sales	$ 31.6
Operating loss	$ (5)

Discontinued Operations - Sch_2

Discontinued Operations - Schedule of Net cash Inflows and Outflows From Discontinued Operations (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Discontinued Operations and Disposal Groups [Abstract]
Net cash provided by operating activities	$ 0.7
Net cash used in investing activities	(0.9)
Effect of exchange rate changes on cash	(0.5)
Net decrease in cash and cash equivalents	$ (0.7)

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Company's Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Fair Value [Member]
Financial assets:
Investments and other assets	$ 1.3	$ 1.3
Financial liabilities:
Long-term debt (including current portion)	801.1	804.1
Carrying Value [Member]
Financial assets:
Investments and other assets	1.3	1.3
Financial liabilities:
Long-term debt (including current portion)	$ 825.3	$ 789.1

Earnings and Dividends per Co_3

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	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Net income attributable to Koppers	$ 63.4	$ 85.2	$ 122
(Loss) gain on sale of discontinued operations, net of tax benefit (expense) of $0.0, $0.1 and $(7.4)	(0.6)	(0.2)	31.9
Income from continuing operations attributable to Koppers	$ 64	$ 85.4	$ 90.1
Weighted average common shares outstanding:
Basic	20,977	21,238	20,992
Effect of dilutive securities	336	687	382
Diluted	21,313	21,925	21,374
Earnings per common share – continuing operations:
Basic earnings per common share	$ 3.05	$ 4.02	$ 4.25
Diluted earnings per common share	$ 3	$ 3.90	$ 4.17
Other data:
Antidilutive securities excluded from computation of diluted earnings per common share	952	436	717

Earnings and Dividends per Co_4

Earnings and Dividends per Common Share - Schedule of Computation of Basic and Diluted Earnings per Common Share (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
(Loss) gain on sale of discontinued operations, tax benefit (expense)	$ 0	$ 0.1	$ (7.4)

Earnings and Dividends per Co_5

Earnings and Dividends per Common Share - Additional Information (Detail) - Subsequent Event [Member]	Feb. 15, 2023 $ / shares
Dividends Payable [Line Items]
Quarterly dividend, declared date	Feb. 15, 2023
Quarterly dividend declared per common share	$ 0.06
Quarterly dividend, payable date	Mar. 27, 2023
Quarterly dividend, payable date of record	Mar. 10, 2023

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future compensation expense related to non-vested stock-based compensation arrangements | $	$ 18.4
Future compensation expense, weighted-average expected period of recognition in months	25 months
Restricted Stock Units (RSUs) [Member] | Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	1 year
Restricted Stock Units (RSUs) [Member] | Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	4 years
Restricted Stock Units (RSUs) [Member] | Employee [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	2 years
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 | shares	0
Stock options, term in years	3 years
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%
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%
Employee Stock Option [Member] | Grants in March 2015 and Thereafter [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, term in years	10 years
Employee Stock Option [Member] | Executive Officer [Member] | Grants in March 2015 and Thereafter [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based awards, vesting period	4 years

Stock-based Compensation - Perf

Stock-based Compensation - Performance Award Fair Value Assumptions (Detail)	12 Months Ended
	Dec. 31, 2022 $ / shares
January 2022 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 32.19
Expected dividend yield per share	0%
Expected volatility	54.50%
Risk-free interest rate	1.52%
Grant date fair value per share of stock performance award	$ 17.58
January 2022 Grant [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 32.19
Expected dividend yield per share	0%
Expected volatility	66.90%
Risk-free interest rate	1.10%
Look-back period in years	3 years
Grant date fair value per share of stock performance award	$ 45.19
January 2021 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 29.84
Expected dividend yield per share	0%
Expected volatility	54.80%
Risk-free interest rate	0.59%
Grant date fair value per share of stock performance award	$ 15.79
January 2021 Grant [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 29.84
Expected dividend yield per share	0%
Expected volatility	68.70%
Risk-free interest rate	0.16%
Look-back period in years	3 years
Grant date fair value per share of stock performance award	$ 41.50
March 2020 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 19.63
Expected dividend yield per share	0%
Expected volatility	42.85%
Risk-free interest rate	0.87%
Grant date fair value per share of stock performance award	$ 8.42
March 2020 Grant [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock performance award	$ 19.63
Expected dividend yield per share	0%
Expected volatility	45.60%
Risk-free interest rate	0.72%
Look-back period in years	2 years 9 months 29 days
Grant date fair value per share of stock performance award	$ 11.56

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Performance Stock Units (Detail) - shares	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	760,625	980,071
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	236,013	474,166
Minimum [Member] | 2021 - 2023 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	67,516
Minimum [Member] | 2022 - 2024 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	18,111
Target Shares [Member] | 2021 - 2023 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	115,972
Target Shares [Member] | 2022 - 2024 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	120,039
Maximum [Member] | 2021 - 2023 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	164,505
Maximum [Member] | 2022 - 2024 [Member] | Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding	220,851

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Status and Activity of Non-Vested Stock Awards (Detail)	12 Months Ended
	Dec. 31, 2022 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	980,071
Granted	403,996
Performance share adjustment	(124,932)
Vested	(459,672)
Forfeited	(38,838)
Non-vested, Ending Balance	760,625
Beginning Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit | $ / shares	$ 30.79
Granted, Weighted Average Grant Date Fair Value per Unit | $ / shares	35.78
Performance share adjustment, Weighted Average Grant Date Fair Value per Unit | $ / shares	25.24
Vested, Weighted Average Grant Date Fair Value per Unit | $ / shares	34.33
Forfeited, Weighted Average Grant Date Fair Value per Unit | $ / shares	27.93
Ending Balance, Non-vested, Weighted Average Grant Date Fair Value per Unit | $ / shares	$ 32.36
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	505,905
Granted	250,760
Performance share adjustment	0
Vested	(202,716)
Forfeited	(29,337)
Non-vested, Ending Balance	524,612
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested, Beginning Balance	474,166
Granted	153,236
Performance share adjustment	(124,932)
Vested	(256,956)
Forfeited	(9,501)
Non-vested, Ending Balance	236,013

Stock-based Compensation - Stoc

Stock-based Compensation - Stock Options Fair Value Assumptions (Detail)	12 Months Ended
	Dec. 31, 2022 $ / shares
January 2022 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock option award	$ 32.19
Expected dividend yield per share	0%
Expected life in years	6 years 9 months 3 days
Expected volatility	54.50%
Risk-free interest rate	1.52%
Grant date fair value per share of stock option award	$ 17.58
January 2021 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock option award	$ 29.84
Expected dividend yield per share	0%
Expected life in years	6 years 7 months 20 days
Expected volatility	54.80%
Risk-free interest rate	0.59%
Grant date fair value per share of stock option award	$ 15.79
March 2020 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock option award	$ 19.63
Expected dividend yield per share	0%
Expected life in years	6 years 4 months 24 days
Expected volatility	42.85%
Risk-free interest rate	0.87%
Grant date fair value per share of stock option award	$ 8.42
March 2019 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date price per share of stock option award	$ 26.63
Expected dividend yield per share	0%
Expected life in years	6 years 1 month 20 days
Expected volatility	39.44%
Risk-free interest rate	2.53%
Grant date fair value per share of stock option award	$ 11.29

Stock-based Compensation - Su_3

Stock-based Compensation - Summary of Status and Activity of Stock Options (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) $ / shares shares
Share-Based Payment Arrangement [Abstract]
Options, Outstanding at December 31, 2021 | shares	1,054,166
Options, Granted | shares	98,108
Options, Expired | shares	(30,138)
Options, Outstanding at December 31, 2022 | shares	1,122,136
Options, Exercisable at December 31, 2022 | shares	843,475
Weighted Average Exercise Price per Option, Outstanding at December 31, 2021 | $ / shares	$ 26.89
Weighted Average Exercise Price per Option, Granted | $ / shares	32.19
Weighted Average Exercise Price per Option, Expired | $ / shares	38.21
Weighted Average Exercise Price per Option, Outstanding at December 31, 2022 | $ / shares	27.05
Weighted Average Exercise Price per Option, Exercisable at December 31, 2022 | $ / shares	$ 26.99
Weighted Average Remaining Contractual Term, Outstanding at December 31, 2022	4 years 7 months 9 days
Weighted Average Remaining Contractual Term, Exercisable at December 31, 2022	3 years 6 months 7 days
Aggregate Intrinsic Value, Outstanding at December 31, 2022 | $	$ 5.5
Aggregate Intrinsic Value, Exercisable at December 31, 2022 | $	$ 4.7

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Stock-based compensation expense recognized:
Less related income tax benefit	$ 4.4	$ 3.7	$ 2.2
Decrease in net income attributable to Koppers	8.8	9.3	9.1
Intrinsic value of exercised stock options	0	2.2	0
Cash received from the exercise of stock options	0	2.3	0
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense recognized:
Stock-based compensation expense	$ 13.2	$ 13	$ 11.3

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) Segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment	3
Net sales	$ 1,980.5	$ 1,678.6	$ 1,669.1
Non-U.S. Countries [Member]
Segment Reporting Information [Line Items]
Net sales	$ 709.4	$ 544.4	$ 499

Segment Information - Summary o

Segment Information - Summary of Results of Segment Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenues from external customers:
Net sales	$ 1,980.5	$ 1,678.6	$ 1,669.1
Depreciation and amortization expense	56.1	57.7	54.1
Items excluded from the determination of segment profit:
Impairment, restructuring and plant closure costs	(1.1)	(4.2)	(15.7)
Gain on sale of assets	2.5	31.2	0
LIFO (expense) benefit	(25.6)	(28.2)	13.7
Mark-to-market commodity hedging (losses) gains	(6.5)	(3.8)	9.2
Inventory adjustment	(1.1)	0	0
Pension settlement	0	0	(0.1)
Discretionary incentive	0	0	(3)
Interest expense	(44.8)	(40.5)	(48.9)
Depreciation and amortization	(56.1)	(57.7)	(54.1)
Depreciation in impairment and restructuring charges	0	(0.7)	(2)
Income tax provision	(31.6)	(34.5)	(21)
Discontinued operations	(0.6)	(0.2)	31.9
Net income	63.2	84.9	121
Capital expenditures:	105.3	125	69.8
Railroad and Utility Products and Services [Member]
Revenues from external customers:
Net sales	788.3	729.9	759.1
Performance Chemicals [Member]
Revenues from external customers:
Net sales	579.9	503.3	526.3
Carbon Materials and Chemicals [Member]
Revenues from external customers:
Net sales	612.3	445.4	383.7
Operating Segments [Member] | Railroad and Utility Products and Services [Member]
Revenues from external customers:
Net sales	788.3	729.9	759.1
Depreciation and amortization expense	22.3	22.3	20.1
Adjusted EBITDA:
Adjusted EBITDA	53.6	45.4	65.3
Items excluded from the determination of segment profit:
Capital expenditures:	47.2	62	31.3
Operating Segments [Member] | Performance Chemicals [Member]
Revenues from external customers:
Net sales	579.9	503.3	526.3
Depreciation and amortization expense	15.3	17.9	18.1
Adjusted EBITDA:
Adjusted EBITDA	75.5	101.8	100.7
Items excluded from the determination of segment profit:
Capital expenditures:	10.6	17.7	12.1
Operating Segments [Member] | Carbon Materials and Chemicals [Member]
Revenues from external customers:
Net sales	612.3	445.4	383.7
Depreciation and amortization expense	18.5	17.5	15.9
Adjusted EBITDA:
Adjusted EBITDA	99	76.3	45
Items excluded from the determination of segment profit:
Capital expenditures:	45.7	42.9	24.8
Intersegment [Member]
Revenues from external customers:
Net sales	96.5	91.2	92.4
Intersegment [Member] | Performance Chemicals [Member]
Revenues from external customers:
Net sales	22.2	15.9	13.7
Intersegment [Member] | Carbon Materials and Chemicals [Member]
Revenues from external customers:
Net sales	74.3	75.3	78.7
Corporate, Non-Segment [Member]
Items excluded from the determination of segment profit:
Capital expenditures:	$ 1.8	$ 2.4	$ 1.6

Segment Information - Summary_2

Segment Information - Summary of Results of Segment Operations (Parenthetical) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Segment Reporting [Abstract]
Net sales	$ 31.6
Depreciation and amortization expense	0.6
Capital expenditure, discontinued operations	$ 0.6

Segment Information - Summary_3

Segment Information - Summary of Tangible and Intangible Assets by Segments (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Asset Reconciling Item [Line Items]
Assets	$ 1,711.4	$ 1,661.9
Deferred taxes	47.7	44.2
Property, plant and equipment, net	557.3	489.1
Operating lease right-of-use assets	86.3	91.2
Goodwill	294	296	$ 297.8
Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	1,678.2	1,628.1
Corporate, Non-Segment [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Prepaid insurance and other assets	16	16.5
Property, plant and equipment, net	6.8	6.6
Operating lease right-of-use assets	10.4	10.7
Railroad and Utility Products and Services [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	660.8	594.1
Goodwill	120.6	120.9
Carbon Materials and Chemicals [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	500.5	447.1
Performance Chemicals [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Goodwill	173.4	175.1	$ 176.7
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Asset Reconciling Item [Line Items]
Assets	516.9	586.9
Goodwill	$ 173.4	$ 175.1

Segment Information - Schedule

Segment Information - Schedule of Revenues and Long-Lived Assets by Geographic Area (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenues from external customers	$ 1,980.5	$ 1,678.6	$ 1,669.1
Long-lived assets	1,062.9	1,018.8	1,015.7
United States [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	1,271.1	1,134.2	1,170.1
Long-lived assets	902.9	857.3	832
Australia [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	283	230.6	194.3
Long-lived assets	73.8	78.9	82
Europe [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	248.9	195.8	162.3
Long-lived assets	67.6	63.3	83.2
Other Countries [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	177.5	118	142.4
Long-lived assets	$ 18.6	$ 19.3	$ 18.5

Segment Information - Schedul_2

Segment Information - Schedule of Revenues and Long-Lived Assets by Geographic Area (Parenthetical) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Segment Reporting Asset Reconciling Item [Line Items]
Net sales	$ 31.6

Segment Information - Schedul_3

Segment Information - Schedule of Segment Revenues for Significant Product Lines (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net sales	$ 1,980.5	$ 1,678.6	$ 1,669.1
Railroad and Utility Products and Services [Member]
Segment Reporting Information [Line Items]
Net sales	788.3	729.9	759.1
Railroad and Utility Products and Services [Member] | Railroad Treated Products [Member]
Segment Reporting Information [Line Items]
Net sales	457.4	414.4	405.1
Railroad and Utility Products and Services [Member] | Utility Poles [Member]
Segment Reporting Information [Line Items]
Net sales	227.9	228	241.7
Railroad and Utility Products and Services [Member] | Rail Joints [Member]
Segment Reporting Information [Line Items]
Net sales	28	22.7	20.3
Railroad and Utility Products and Services [Member] | Railroad Infrastructure Services [Member]
Segment Reporting Information [Line Items]
Net sales	61.8	56	63.5
Railroad and Utility Products and Services [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	13.2	8.8	28.6
Carbon Materials and Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	612.3	445.4	383.7
Carbon Materials and Chemicals [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	13.6	30.3	26.7
Carbon Materials and Chemicals [Member] | Pitch and Related Products [Member]
Segment Reporting Information [Line Items]
Net sales	390.7	260.3	230.9
Carbon Materials and Chemicals [Member] | Creosote and Distillates [Member]
Segment Reporting Information [Line Items]
Net sales	62.9	52.1	40
Carbon Materials and Chemicals [Member] | Phthalic Anhydride and Other Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	109.1	75.6	66.4
Carbon Materials and Chemicals [Member] | Naphthalene [Member]
Segment Reporting Information [Line Items]
Net sales	36	27.1	19.7
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales	579.9	503.3	526.3
Performance Chemicals [Member] | Other Products [Member]
Segment Reporting Information [Line Items]
Net sales	18.7	14.2	15.6
Performance Chemicals [Member] | Wood Preservative Products [Member]
Segment Reporting Information [Line Items]
Net sales	$ 561.2	$ 489.1	$ 510.7

Segment Information - Schedul_4

Segment Information - Schedule of Segment Revenues for Significant Product Lines (Parenthetical) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Segment Reporting [Abstract]
Net sales	$ 31.6

Income Taxes - Summary of Incom

Income Taxes - Summary of Income Tax Provision (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Current:
Federal	$ 0	$ (1.5)	$ 0.8
State	0.6	0.9	0.7
Foreign	28.4	18.2	11.1
Total current tax provision	29	17.6	12.6
Deferred:
Federal	0.2	10.6	6.1
State	(0.6)	1.1	1.6
Foreign	3	5.2	0.7
Total deferred tax provision	2.6	16.9	8.4
Total income tax provision	$ 31.6	$ 34.5	$ 21

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Income before income taxes	$ 106.8	$ 71.8	$ 52.4
Valuation allowance	$ 43.8	44.5
Valuation allowance				$ 13.3
Percentage of allowable business interest expense deduction from adjusted taxable income	50%
Income tax expense (benefit)	$ 31.6	34.5	21
Unrealized (gains) losses on cash flow hedges to expense, tax benefit (expense)	(6.1)	(0.5)	12.6
Deferred income tax benefit (expense) relating to unfunded status of employee post-retirement benefit plans	(0.5)	1.3	0.4
Unremitted earnings	518
Unrecognized tax benefits with impact on the effective tax rate	1.4	1.5
Interest expense (income) and related penalties	(0.1)
Accrued interest expense and penalties	0.3	0.4
Copper Swap Contracts [Member]
Income Taxes [Line Items]
Unrealized (gains) losses on cash flow hedges to expense, tax benefit (expense)	6.1	0.5	(12.6)
Foreign and State Tax [Member]
Income Taxes [Line Items]
Valuation allowance	$ 0.9
Reverse Valuation Allowance Carryforward [Member]
Income Taxes [Line Items]
Income tax expense (benefit)			$ (13.3)
Foreign [Member] | United Kingdom [Member]
Income Taxes [Line Items]
Valuation allowance		$ 3.3

Income Taxes - Summary of Inc_2

Income Taxes - Summary of Income Taxes Reconciled with Federal Statutory Rate (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Federal income tax rate	21%	21%	21%
Foreign earnings taxed at different rates	8.70%	4.30%	2.90%
GILTI inclusion, net of foreign tax credits	1.70%	0.20%	4%
Valuation allowance adjustments	0.90%	1.90%	(12.10%)
Deferred tax adjustments	0%	(0.20%)	(2.20%)
Change in tax contingency reserves	(0.10%)	(1.10%)	(0.20%)
State income taxes, net of federal tax benefit	(0.20%)	2.10%	2.20%
Other	1.10%	0.60%	3.50%
Total effective tax rate	33.10%	28.80%	19.10%

Income Taxes - Summary of Defer

Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Federal and state tax loss carryforwards, expiring from 2021 to 2040	$ 22.6	$ 24.4
Tax credits	17.4	17.5
Reserves, including insurance and environmental	9.3	9
Pension and other postretirement benefits obligations	8.2	9.6
Foreign tax loss carryforwards	6.6	7.4
Accrued employee compensation	6.5	7.1
Interest disallowance	6.4	0
Asset retirement obligations	5.3	4.5
Inventory	4.6	5.9
Other	4.6	3.3
Valuation allowance	(43.8)	(44.5)
Total deferred tax assets	47.7	44.2
Deferred tax liabilities:
Tax over book depreciation and amortization	52.3	44
Gain on derivative contracts	0.7	14.3
Other	4.5	4.3
Total deferred tax liabilities	57.5	62.6
Net deferred tax liabilities	$ (9.8)	$ (18.4)

Income Taxes - Summary of Valua

Income Taxes - Summary of Valuation Allowances Recorded to Offset Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
Total valuation allowances	$ 43.8	$ 44.5
Foreign [Member] | Tax Credits [Member]
Income Taxes [Line Items]
Total valuation allowances	16.1	16.1
Foreign [Member] | Operating Losses and Capital Losses [Member]
Income Taxes [Line Items]
Total valuation allowances	8.3	9.1
State [Member] | Operating Losses and Tax Credits [Member]
Income Taxes [Line Items]
Total valuation allowances	19.4	19.2
Federal [Member]
Income Taxes [Line Items]
Total valuation allowances	$ 0	$ 0.1

Income taxes - Summary of Unrec

Income taxes - Summary of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 1.5	$ 2.5	$ 2.1
Additions based on tax provisions related to the current year	0.1	0.1	0.2
Additions for tax provisions of prior years	0	0	0.5
Reductions resulting from a lapse in the statute of limitations	(0.2)	(1.1)	(0.3)
Balance at end of year	$ 1.4	$ 1.5	$ 2.5

Inventories - Components of Inv

Inventories - Components of Inventories (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Inventory Disclosure [Abstract]
Raw materials	$ 318.5	$ 266.8
Work in process	10.2	12.6
Finished goods	130.4	112.1
Inventories, gross	459.1	391.5
Less revaluation to LIFO	103.4	77.7
Inventories, net	$ 355.7	$ 313.8

Property, Plant and Equipment -

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,019.4	$ 927.8
Less accumulated depreciation	462.1	438.7
Property, plant and equipment, net	557.3	489.1
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15	15.2
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	80.3	75.8
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 924.1	$ 836.8

Property, Plant and Equipment_2

Property, Plant and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 41,200,000	$ 39,400,000	$ 33,700,000
Depreciation Expense Excludes KJCC Discontinued Operations			600,000
Impairment charges	$ 0	$ 0	$ 0

Goodwill and Other Identifiab_3

Goodwill and Other Identifiable Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	$ 296	$ 297.8
Currency translation	(2)	(1.8)
Balance ending	294	296
Performance Chemicals [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	175.1	176.7
Currency translation	(1.7)	(1.6)
Balance ending	173.4	175.1
Railroad Products and Services [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	41.1	41.1
Currency translation	(0.1)	0
Balance ending	41	41.1
Utility Products [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Balance beginning	79.8	80
Currency translation	(0.2)	(0.2)
Balance ending	$ 79.6	$ 79.8

Goodwill and Other Identifiab_4

Goodwill and Other Identifiable Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment charge	$ 0	$ 0	$ 0
Decrease in carrying value of identifiable intangible assets	2,100,000
Amortization expense	$ 14,900,000	$ 18,300,000	$ 19,800,000

Goodwill and Other Identifiab_5

Goodwill and Other Identifiable Intangible Assets - Schedule of Identifiable Intangible Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	8 years 10 months 24 days
Gross Carrying Amount	$ 263	$ 265.1
Accumulated Amortization	146.9	133.6
Net	$ 116.1	131.5
Customer Contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	9 years
Gross Carrying Amount	$ 224.9	226.9
Accumulated Amortization	110.5	97.6
Net	$ 114.4	129.3
Customer Contracts [Member] | Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	9 years
Customer Contracts [Member] | Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	18 years
Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	3 years 7 months 6 days
Gross Carrying Amount	$ 26.4	26.5
Accumulated Amortization	26	25.9
Net	$ 0.4	0.6
Technology [Member] | Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	4 years
Technology [Member] | Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	12 years
Trademarks [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average remaining life in years	11 years
Gross Carrying Amount	$ 7.7	7.6
Accumulated Amortization	6.5	6.4
Net	$ 1.2	1.2
Trademarks [Member] | Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	2 years
Trademarks [Member] | Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	18 years
Supply Contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	10 years
Weighted average remaining life in years	0 years
Gross Carrying Amount	$ 2.4	2.4
Accumulated Amortization	2.4	2.4
Net	$ 0	0
Non-Compete Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated life in years	12 years
Weighted average remaining life in years	1 year 9 months 18 days
Gross Carrying Amount	$ 1.6	1.7
Accumulated Amortization	1.5	1.3
Net	$ 0.1	$ 0.4

Goodwill and Other Identifiab_6

Goodwill and Other Identifiable Intangible Assets - Schedule of Future Amortization Expense (Detail) $ in Millions	Dec. 31, 2022 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2023	$ 14.4
2024	14.2
2025	13.7
2026	12.4
2027	$ 12

Pensions and Post-Retirement _3

Pensions and Post-Retirement Benefit Plans - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) Plan	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of domestic non-qualified defined benefit plans | Plan	3
Defined contribution plan expense	$ 8.4	$ 9.1	$ 8.4
Net actuarial loss	51.8
Fair value of pension plan assets	127.4	190
Premium payment		67.8
Pension settlement loss		20
Accumulated benefit obligation, pension plans	156.8	219.1
Expenses incurred	12.6	14.9	17.3
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	51.8	9
Fair value of pension plan assets	127.4	190	208
Benefit obligation	157	219.6	233.3
Expected contributions by employer	0
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	3.4	0.6
Fair value of pension plan assets	0	0	0
Benefit obligation	6	$ 9.8	$ 10.5
Expected contributions by employer	0.6
United States [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment losses	32.3
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	32.6
Plan assets	31.6
Annuity Insurance policy [Member] | United Kingdom [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Revaluation decrease	13.6
Annuity Insurance policy [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 31.6
Growth seeking assets [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation investment strategy	30%
Growth seeking assets [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation investment strategy	40%
Income generating assets [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation investment strategy	60%
Income generating assets [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation investment strategy	70%
Salaried and Hourly Employees [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of domestic non-qualified defined benefit plans | Plan	2

Pensions and Post-Retirement _4

Pensions and Post-Retirement Benefit Plans - Components of Net Periodic Benefit Cost for Pension Plans and Other Benefit Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.2	$ 1.5	$ 1.4
Interest cost	5.6	5.2	6.4
Expected return on plan assets	(7.7)	(7.4)	(7.9)
Amortization of net loss (gain)	1.8	1.4	1.7
Settlements and curtailments	0	0	0.1
Net periodic benefit cost	$ 0.9	$ 0.7	$ 1.7
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0.1	$ 0.1
Interest cost	0.3	0.3	0.3
Expected return on plan assets	0	0	0
Amortization of net loss (gain)	(0.1)	0	(0.2)
Settlements and curtailments	0	0	0
Net periodic benefit cost	$ 0.2	$ 0.4	$ 0.2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax

Pensions and Post-Retirement _5

Pensions and Post-Retirement Benefit Plans - Schedule of Change in Funded Status of Pension and Post-Retirement Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Actuarial gains	$ (51.8)
Fair value of plan assets at beginning of year	190
Fair value of plan assets at end of year	127.4	$ 190
Noncurrent liabilities	34.7	38.6
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	219.6	233.3
Service cost	1.2	1.5	$ 1.4
Interest cost	5.6	5.2	6.4
Actuarial gains	(51.8)	(9)
Settlements	(1)	0
Currency translation	(5.8)	(0.6)
Benefits paid	(10.8)	(10.8)
Benefit obligation at end of year	157	219.6	233.3
Fair value of plan assets at beginning of year	190	208
Actual return on plan assets	(46.1)	(8.9)
Employer contribution	0.9	2.3
Settlements	(1)	0
Currency translation	(5.6)	(0.6)
Benefits paid	(10.8)	(10.8)
Fair value of plan assets at end of year	127.4	190	208
Funded status of the plan	(29.6)	(29.6)
Noncurrent assets	0.6	0.8
Current liabilities	1	1
Noncurrent liabilities	29.2	29.4
Benefit obligation	154.4	215.7
Fair value of plan assets	124.2	185.3
Accumulated benefit obligation	154.2	215.5
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	9.8	10.5
Service cost	0	0.1	0.1
Interest cost	0.3	0.3	0.3
Actuarial gains	(3.4)	(0.6)
Settlements	0	0
Currency translation	0	0
Benefits paid	(0.7)	(0.5)
Benefit obligation at end of year	6	9.8	10.5
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contribution	0.7	0.5
Settlements	0	0
Currency translation	0	0
Benefits paid	(0.7)	(0.5)
Fair value of plan assets at end of year	0	0	$ 0
Funded status of the plan	(6)	(9.8)
Noncurrent assets	0	0
Current liabilities	0.5	0.6
Noncurrent liabilities	$ 5.5	$ 9.2

Pensions and Post-Retirement _6

Pensions and Post-Retirement Benefit Plans - Schedule of Projected Benefit Payments (Detail) $ in Millions	Dec. 31, 2022 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2023	$ 11.6
2024	11.3
2025	11.8
2026	11.3
2027	11.2
Next five years	57.9
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2023	0.5
2024	0.5
2025	0.5
2026	0.5
2027	0.5
Next five years	$ 2.4

Pensions and Post-Retirement _7

Pensions and Post-Retirement Benefit Plans - Schedule of Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.42%	2.67%
Expected return on plan assets	4.65%	3.91%
Rate of compensation increase	3.13%	3%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.58%	2.97%
Initial medical trend rate	5.40%	5.40%

Pensions and Post-Retirement _8

Pensions and Post-Retirement Benefit Plans - Schedule of Weighted Average Asset Allocation for Company's Pension Plans (Detail)	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
December 31,	100%	100%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
December 31,	52%	49%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
December 31,	20%	21%
Other [Member]
Defined Benefit Plan Disclosure [Line Items]
December 31,	28%	30%

Pensions and Post-Retirement _9

Pensions and Post-Retirement Benefit Plans - Schedule of Pension Plan Assets at Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 127.4	$ 190
Investments measured at NAV	36	40.7
Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	91.4	149.3
Fair Value, Recurring | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value, Recurring | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	59.9	97
Fair Value, Recurring | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	31.5	52.3
Fair Value, Recurring | U.S. equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	4.9	7.9
Fair Value, Recurring | U.S. equity securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value, Recurring | U.S. equity securities [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	4.9	7.9
Fair Value, Recurring | U.S. equity securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value, Recurring | Insurance Annuity Contract and Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	32
Fair Value, Recurring | Insurance Annuity Contract and Other Investments [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0
Fair Value, Recurring | Insurance Annuity Contract and Other Investments [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.5
Fair Value, Recurring | Insurance Annuity Contract and Other Investments [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	31.5
Fair Value, Recurring | International equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	11.1	17.9
Fair Value, Recurring | International equity securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value, Recurring | International equity securities [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	11.1	17.9
Fair Value, Recurring | International equity securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value, Recurring | U.S. debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	39.2	64.9
Fair Value, Recurring | U.S. debt securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value, Recurring | U.S. debt securities [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	39.2	64.9
Fair Value, Recurring | U.S. debt securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value, Recurring | International debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2.6	3.6
Fair Value, Recurring | International debt securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value, Recurring | International debt securities [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2.6	3.6
Fair Value, Recurring | International debt securities [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value, Recurring | Cash & Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.6	2.1
Fair Value, Recurring | Cash & Cash Equivalents [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value, Recurring | Cash & Cash Equivalents [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.6	2.1
Fair Value, Recurring | Cash & Cash Equivalents [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 0	0
Fair Value, Recurring | Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		52.9
Fair Value, Recurring | Other Investments [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0
Fair Value, Recurring | Other Investments [Member] | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0.6
Fair Value, Recurring | Other Investments [Member] | Significant unobservable inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		$ 52.3

Debt - Schedule of Long-Term De

Debt - Schedule of Long-Term Debt Instruments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Total debt	$ 825.3	$ 789.1
Less short-term debt and current maturities of long-term debt	0	2
Less unamortized debt issuance costs	7.6	5.6
Long-term debt	817.7	781.5
Term Loan [Member]
Debt Instrument [Line Items]
Total debt	0	2
2.38 percent Revolving Credit Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Total debt	$ 0	287.1
6.72 Percent Revolving Credit Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.72%
Debt, Maturity	2027
Total debt	$ 325.3	0
6.00 percent Senior Notes due 2025 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6%
Debt, Maturity	2025
Total debt	$ 500	$ 500

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($)		1 Months Ended	12 Months Ended
	Feb. 15, 2022	Jun. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Revolving credit facility		$ 730,000,000
Long term debt			$ 825,300,000	$ 789,100,000
Accumulated amortization			14,900,000	12,100,000
Unamortized debt issuance costs			7,600,000	5,600,000
Senior Secured Credit Facilities [Member]
Debt Instrument [Line Items]
Letters of credit, amount outstanding			$ 7,800,000
6.00 percent Senior Notes due 2025 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes, payment terms			The 2025 Notes pay interest semi-annually in arrears on February 15 and August 15 and will mature on February 15, 2025 unless earlier redeemed or repurchased.
Long term debt			$ 500,000,000	$ 500,000,000
Debt instrument, redemption price percentage	101.50%
Debt maturity date			Feb. 15, 2025
Revolving Credit Agreement [Member]
Debt Instrument [Line Items]
Revolving credit facility		$ 800,000,000
Credit facility maturity date		Jun. 17, 2027
Senior Secured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility		$ 600,000,000
Senior Secured Term Loan Facility [Member]
Debt Instrument [Line Items]
Secured term loan		100,000,000
Swingline Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility		$ 50,000,000
Revolving Credit Facility [Member] | Senior Secured Credit Facilities [Member]
Debt Instrument [Line Items]
Debt instrument, unused borrowing capacity			$ 412,000,000

Debt - Schedule of Debt Maturit

Debt - Schedule of Debt Maturities (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Disclosure [Abstract]
2023	$ 0
2024	0
2025	500
2026	0
2027	325.3
Total debt	$ 825.3	$ 789.1

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Operating lease costs	$ 29.3	$ 30.2
Variable lease costs	$ 3.3	$ 3.3

Leases - Summary of Amount and

Leases - Summary of Amount and Timing of Cash Flows From Operating Leases (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
2023	$ 26.2
2024	22.3
2025	17.1
2026	12.3
2027	10
Thereafter	20.6
Total lease payments	108.5
Less: Interest	(21.7)
Present value of lease liabilities	$ 86.8	$ 91.6

Leases - Schedule of Supplement

Leases - Schedule of Supplemental Consolidated Balance Sheet Information Related to Leases (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Operating leases:
Operating lease right-of-use assets	$ 86.3	$ 91.2
Current operating lease liabilities	20.5	21.3
Operating lease liabilities	66.3	70.3
Total operating lease liabilities	$ 86.8	$ 91.6
Weighted average remaining lease term, in years	5 years 7 months 6 days	5 years 9 months 18 days
Weighted average discount rate	7.20%	7.40%

Derivative Financial Instrume_3

Derivative Financial Instruments - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Maximum period hedged in cash flow hedge	36 months
Unrealized gains, reclassification period	12 months
Unrealized gains, net of tax, expected to be reclassified from other comprehensive income into earnings	$ 1.6

Derivative Financial Instrume_4

Derivative Financial Instruments - Schedule of Outstanding Copper Swap Contracts (Detail) - Copper Swap Contracts [Member] £ in Millions, $ in Millions	Dec. 31, 2022 GBP (£)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 GBP (£)	Dec. 31, 2021 USD ($)
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding | £	£ 27.3		£ 35.1
Net Fair Value - Asset | $		$ 3.1		$ 60.9
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding | £	21.3		29
Net Fair Value - Asset | $		2.5		53.8
Not Designated as Hedging Instrument [Member]
Derivatives Fair Value [Line Items]
Copper Swap Contracts Units Outstanding | £	£ 6		£ 6.1
Net Fair Value - Asset | $		$ 0.6		$ 7.1

Derivative Financial Instrume_5

Derivative Financial Instruments - Schedule of Fair Value of Outstanding Copper Swap Contracts Recorded in Balance Sheet (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Accumulated other comprehensive gain, net of tax	$ (38.8)	$ (3.8)	$ 41.2
Copper Swap Contracts [Member]
Derivative [Line Items]
Net Fair Value - Asset (Liability)	3.1	60.9
Accumulated other comprehensive gain, net of tax	1.8	40.6
Copper Swap Contracts [Member] | Accrued Liabilities [Member]
Derivative [Line Items]
Net Fair Value - Asset (Liability)	(0.3)	0
Copper Swap Contracts [Member] | Derivative Contracts [Member]
Derivative [Line Items]
Net Fair Value - Asset (Liability)	$ 3.4	$ 60.9

Derivative Financial Instrume_6

Derivative Financial Instruments - Schedule of Unrealized Gain (Loss) from Contract Where Hedge Accounting Was Not Elected (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Hedges [Member] | Contracts Where Hedge Accounting Was not Elected [Member]
Derivative [Line Items]
(Loss) gain from contracts where hedge accounting was not elected	$ (6.5)	$ (3.8)	$ 9.2

Derivative Financial Instrume_7

Derivative Financial Instruments - Schedule of Fair Value of Outstanding Foreign Currency Forward Contracts (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Not designated gross derivative liability	$ 0	$ (0.3)
Forward Contracts [Member] | Accrued Liabilities [Member]
Derivative [Line Items]
Not designated gross derivative liability	(0.1)	(0.5)
Forward Contracts [Member] | Derivative Contracts [Member]
Derivative [Line Items]
Not designated gross derivative liability	$ 0.1	$ 0.1

Derivative Financial Instrume_8

Derivative Financial Instruments - Summary of Net Currency Units Outstanding (Detail)	Dec. 31, 2022 NZD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 NZD ($)	Dec. 31, 2021 USD ($)
Offsetting [Abstract]
Net currency units outstanding	$ 3,300,000	$ 9,300,000	$ 0	$ 21,400,000

Common Stock and Senior Conve_3

Common Stock and Senior Convertible Preferred Stock - Schedule of Changes in Senior Convertible Preferred Stock, Common Stock and Treasury Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Equity [Abstract]
Senior Convertible Preferred Stock, balance at beginning and end of year	0	0	0
Common Stock, balance at beginning of year	24,026,844	23,688,000	23,321,000
Common Stock, issued for employee stock plans	520,000	339,000	367,000
Common Stock, balance at end of year	24,547,000	24,026,844	23,688,000
Treasury Stock, balance at beginning of year	(2,930,694)	(2,590,000)	(2,516,000)
Treasury Stock, shares repurchased	(853,000)	(341,000)	(74,000)
Treasury Stock, balance at end of year	(3,783,901)	(2,930,694)	(2,590,000)

Commitments and Contingent Li_3

Commitments and Contingent Liabilities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2022 USD ($) Plant Plaintiff Case Site State Party	Dec. 31, 2021 USD ($) Case Plaintiff	Dec. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Number of states with new claims filed | State	2
Number of plaintiffs | Plaintiff	51	59
Environmental remediation and regulation liability	$ 10,900,000	$ 10,700,000	$ 11,000,000
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]	Liabilities, Current
Accrued liability for environmental matters, current	$ 2,500,000	$ 2,800,000
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	$ 4,100,000
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	31
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
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	$ 3,900,000
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	$ 1,300,000

Commitments and Contingent Li_4

Commitments and Contingent Liabilities - Changes in Accrued Liability for Environmental Matters (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Balance at beginning of year	$ 10.7	$ 11
Expense	1.6	0.3
Revision of reserves	0	(0.1)
Cash expenditures	(1.1)	(0.4)
Currency translation	(0.3)	(0.1)
Balance at end of period	$ 10.9	$ 10.7

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 3.3	$ 2.6	$ 2.6
Increase (Decrease) to Expense	0.3	1.2	0.2
Net Write-Offs	(0.1)	(0.5)	(0.2)
Currency Translation	0	0	0
Balance at End of Year	3.5	3.3	2.6
Deferred Tax Valuation Allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	44.5	44.6	58
Increase (Decrease) to Expense	0.9	3.6	(12.1)
Net Write-Offs	(0.9)	(3.6)	(1.7)
Currency Translation	(0.7)	(0.1)	0.4
Balance at End of Year	$ 43.8	$ 44.5	$ 44.6