Kaiser Aluminum (KALU) 10-Q 28 Jul 20 2020 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 20, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
Document Transition Report	false
Entity File Number	1-09447
Entity Registrant Name	KAISER ALUMINUM CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	94-3030279
Entity Address, Address Line One	27422 Portola Parkway
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	Foothill Ranch
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92610-2831
City Area Code	(949)
Local Phone Number	614-1740
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Common stock, par value $0.01 per share
Trading Symbol	KALU
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		15,812,169
Entity Central Index Key	0000811596
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS (UN

CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 710.6	$ 264.3
Short-term investments		78.7
Receivables:
Trade receivables, net	126.4	167.1
Other	22	18.1
Contract assets	41.6	54.6
Inventories	181.4	177.6
Prepaid expenses and other current assets	25.7	19.4
Total current assets	1,107.7	779.8
Property, plant and equipment, net	627.1	622
Operating lease assets	28	25.8
Deferred tax assets, net		11.8
Intangible assets, net	28.1	29.6
Goodwill	18.8	18.8
Other assets	38.7	38.4
Total	1,848.4	1,526.2
Current liabilities:
Accounts payable	61	92
Accrued salaries, wages and related expenses	34.9	34.4
Other accrued liabilities	54.5	44
Total current liabilities	150.4	170.4
Long-term portion of operating lease liabilities	27	25.2
Net liabilities of Salaried VEBA	32.5	32.6
Deferred tax liabilities	7.3	4.5
Long-term liabilities	75.3	67
Long-term debt	837.1	492.6
Total liabilities	1,129.6	792.3
Commitments and contingencies
Stockholders' equity:
Preferred stock, 5,000,000 shares authorized at both June 30, 2020 and December 31, 2019; no shares were issued and outstanding at June 30, 2020 and December 31, 2019
Common stock, par value $0.01, 90,000,000 shares authorized at both June 30, 2020 and at December 31, 2019; 22,647,455 shares issued and 15,812,169 shares outstanding at June 30, 2020; 22,550,827 shares issued and 15,868,304 shares outstanding at December 31, 2019	0.2	0.2
Additional paid in capital	1,063.3	1,062.9
Retained earnings	173.4	172.8
Treasury stock, at cost, 6,835,286 shares at June 30, 2020 and 6,682,523 shares at December 31, 2019, respectively	(475.9)	(463.4)
Accumulated other comprehensive loss	(42.2)	(38.6)
Total stockholders' equity	718.8	733.9
Total	$ 1,848.4	$ 1,526.2

CONSOLIDATED BALANCE SHEETS (_2

CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	90,000,000	90,000,000
Common Stock, shares issued	22,647,455	22,550,827
Common stock, shares outstanding	15,812,169	15,868,304
Treasury stock, shares	6,835,286	6,682,523

STATEMENTS OF CONSOLIDATED (LOS

STATEMENTS OF CONSOLIDATED (LOSS) INCOME (UNAUDITED) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Net sales	$ 275.7	$ 375.3	$ 645	$ 770.5
Costs and expenses:
Cost of products sold, excluding depreciation and amortization and other items	224.5	303.5	511.1	618.6
Depreciation and amortization	13	12.1	26.2	24
Selling, general, administrative, research and development	22.7	27.2	46.6	52.4
Restructuring costs	11.9		11.9
Other operating (income) charges, net	(1.1)	0.1	(1.1)	0.1
Total costs and expenses	271	342.9	594.7	695.1
Operating income	4.7	32.4	50.3	75.4
Other income (expense):
Interest expense	(10.5)	(5.8)	(16.6)	(11.5)
Other income (expense), net	0.5	(0.1)	(0.3)	0.4
(Loss) income before income taxes	(5.3)	26.5	33.4	64.3
Income tax provision	(1.3)	(7.3)	(10.9)	(17.1)
Net (loss) income	$ (6.6)	$ 19.2	$ 22.5	$ 47.2
Net (loss) income per common share:
Basic	$ (0.41)	$ 1.19	$ 1.42	$ 2.93
Diluted	$ (0.41)	$ 1.18	$ 1.41	$ 2.89
Weighted-average number of common shares outstanding (in thousands):
Basic	15,781	16,063	15,809	16,085
Diluted	15,781	16,240	15,929	16,298

STATEMENTS OF CONSOLIDATED COMP

STATEMENTS OF CONSOLIDATED COMPREHENSIVE INCOME (LOSS) (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (6.6)	$ 19.2	$ 22.5	$ 47.2
Other comprehensive income (loss), net of tax
Defined benefit pension plan and Salaried VEBA	0.9	1.1	2	2.2
Available for sale securities	(0.3)	(0.1)	(0.5)	(0.3)
Cash flow hedges	10.8	(4.2)	(5.1)	4.6
Fair value hedges	0.5
Other comprehensive income (loss), net of tax	11.9	(3.2)	(3.6)	6.5
Comprehensive income	$ 5.3	$ 16	$ 18.9	$ 53.7

STATEMENTS OF CONSOLIDATED STOC

STATEMENTS OF CONSOLIDATED STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions		Total	Common Stock	Additional Paid in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2018		$ 740.4	$ 0.2	$ 1,059.3	$ 150.2	$ (420.5)	$ (48.8)
Beginning balance (shares) at Dec. 31, 2018			16,234,603
Stockholders' Equity [Roll Forward]
Net (loss) income		28			28
Other comprehensive income (loss), net of tax		9.7					9.7
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			122,309
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(5)		(5)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(46,388)
Repurchase of common stock	[1]	(17.4)				(17.4)
Repurchase of common stock (shares)	[1]		(175,977)
Cash dividends declared	[2]	(10.2)			(10.2)
Amortization of unearned equity compensation		2.4		2.4
Ending balance at Mar. 31, 2019		747.9	$ 0.2	1,056.7	168	(437.9)	(39.1)
Ending balance (shares) at Mar. 31, 2019			16,134,547
Beginning balance at Dec. 31, 2018		740.4	$ 0.2	1,059.3	150.2	(420.5)	(48.8)
Beginning balance (shares) at Dec. 31, 2018			16,234,603
Stockholders' Equity [Roll Forward]
Net (loss) income		47.2
Other comprehensive income (loss), net of tax		6.5
Ending balance at Jun. 30, 2019		746.3	$ 0.2	1,059.2	177.3	(448.1)	(42.3)
Ending balance (shares) at Jun. 30, 2019			16,028,675
Beginning balance at Mar. 31, 2019		747.9	$ 0.2	1,056.7	168	(437.9)	(39.1)
Beginning balance (shares) at Mar. 31, 2019			16,134,547
Stockholders' Equity [Roll Forward]
Net (loss) income		19.2			19.2
Other comprehensive income (loss), net of tax		(3.2)					(3.2)
Common shares issued (including impacts from Long-Term Incentive programs)		0.3		0.3
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			14,700
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(1.2)		(1.2)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(12,395)
Repurchase of common stock	[1]	(10.2)				(10.2)
Repurchase of common stock (shares)	[1]		(108,177)
Cash dividends declared	[2]	(9.9)			(9.9)
Amortization of unearned equity compensation		3.4		3.4
Ending balance at Jun. 30, 2019		746.3	$ 0.2	1,059.2	177.3	(448.1)	(42.3)
Ending balance (shares) at Jun. 30, 2019			16,028,675
Beginning balance at Dec. 31, 2019		$ 733.9	$ 0.2	1,062.9	172.8	(463.4)	(38.6)
Beginning balance (shares) at Dec. 31, 2019		15,868,304	15,868,304
Stockholders' Equity [Roll Forward]
Net (loss) income		$ 29.1			29.1
Other comprehensive income (loss), net of tax		(15.5)					(15.5)
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[3]		119,598
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(4.3)		(4.3)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(45,545)
Repurchase of common stock	[4]	(12.5)				(12.5)
Repurchase of common stock (shares)	[4]		(152,763)
Cash dividends declared	[5]	(11.3)			(11.3)
Amortization of unearned equity compensation		1.7		1.7
Ending balance at Mar. 31, 2020		721.1	$ 0.2	1,060.3	190.6	(475.9)	(54.1)
Ending balance (shares) at Mar. 31, 2020			15,789,594
Beginning balance at Dec. 31, 2019		$ 733.9	$ 0.2	1,062.9	172.8	(463.4)	(38.6)
Beginning balance (shares) at Dec. 31, 2019		15,868,304	15,868,304
Stockholders' Equity [Roll Forward]
Net (loss) income		$ 22.5
Other comprehensive income (loss), net of tax		(3.6)
Ending balance at Jun. 30, 2020		$ 718.8	$ 0.2	1,063.3	173.4	(475.9)	(42.2)
Ending balance (shares) at Jun. 30, 2020		15,812,169	15,812,169
Beginning balance at Mar. 31, 2020		$ 721.1	$ 0.2	1,060.3	190.6	(475.9)	(54.1)
Beginning balance (shares) at Mar. 31, 2020			15,789,594
Stockholders' Equity [Roll Forward]
Net (loss) income		(6.6)			(6.6)
Other comprehensive income (loss), net of tax		11.9					11.9
Common shares issued (including impacts from Long-Term Incentive programs)	[3]	0.4		0.4
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[3]		22,575
Repurchase of common stock (shares)			0
Cash dividends declared	[5]	(10.6)			(10.6)
Amortization of unearned equity compensation		2.6		2.6
Ending balance at Jun. 30, 2020		$ 718.8	$ 0.2	$ 1,063.3	$ 173.4	$ (475.9)	$ (42.2)
Ending balance (shares) at Jun. 30, 2020		15,812,169	15,812,169
[1]	Weighted-average repurchase price (dollars per share) for the quarters ended March 31, 2019 and June 30, 2019 was $98.55
[2]	Dividends declared per common share were $0.60
[3]	At June 30, 2020, 358,122
[4]	Weighted-average repurchase price (dollars per share) for the quarter ended March 31, 2020 was $81.94. There was no repurchase of common stock for the quarter ended June 30, 2020. At June 30, 2020, $93.1
[5]	Dividends declared per common share was $0.67 for each of the quarters ended March 31, 2020 and June 30, 2020.

STATEMENTS OF CONSOLIDATED ST_2

STATEMENTS OF CONSOLIDATED STOCKHOLDERS' EQUITY (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Mar. 31, 2020		Jun. 30, 2019		Mar. 31, 2019
Shares available for awards (shares)	358,122
Weighted average repurchase price (in dollars per share)		$ 81.94		$ 95		$ 98.55
Repurchase amount remaining	$ 93.1
Cash dividends declared (in dollars per share)	$ 0.67	$ 0.67		$ 0.60		$ 0.60
Common Stock
Repurchase of common stock	0	152,763	[1]	108,177	[2]	175,977	[2]
[1]	Weighted-average repurchase price (dollars per share) for the quarter ended March 31, 2020 was $81.94. There was no repurchase of common stock for the quarter ended June 30, 2020. At June 30, 2020, $93.1
[2]	Weighted-average repurchase price (dollars per share) for the quarters ended March 31, 2019 and June 30, 2019 was $98.55

STATEMENTS OF CONSOLIDATED CASH

STATEMENTS OF CONSOLIDATED CASH FLOWS (UNAUDITED) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net (loss) income		$ 22.5	$ 47.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property, plant and equipment		24.8	22.6
Amortization of definite-lived intangible assets		1.4	1.4
Amortization of debt premium and debt issuance costs		0.8	0.6
Deferred income taxes		15.8	18.3
Non-cash equity compensation		4.7	6.1
Gain on disposition of short-term investments		(0.7)	(0.4)
Non-cash asset impairment charge		0	0.1
Loss (gain) on disposition of property, plant and equipment		0.3	(0.2)
Other non-cash changes in assets and liabilities		3.1	6.1
Changes in operating assets and liabilities:
Trade and other receivables		36.5	2.2
Contract assets		13	8
Inventories		(3.8)	(16)
Prepaid expenses and other current assets		(7.6)	(4.3)
Accounts payable		(28.7)	(13.4)
Accrued liabilities		10.9	(6.6)
Annual variable cash contributions to Salaried VEBA		(2.9)	(2.1)
Long-term assets and liabilities, net		4.8	0.9
Net cash provided by operating activities	[1]	94.9	70.5
Cash flows from investing activities:
Capital expenditures		(31.8)	(29.9)
Purchase of short-term investments		(39.1)	(33)
Purchase of equity securities		(0.5)	(0.7)
Proceeds from disposition of short-term investments		118.1	45.7
Proceeds from disposition of property, plant and equipment		0	0.2
Net cash provided by (used in ) investing activities	[1]	46.7	(17.7)
Cash flows from financing activities:
Issuance of 6.50% Senior Notes		350	0
Cash paid for debt issuance costs		(6.1)	0
Repayment of finance lease		(0.8)	(0.6)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(4.3)	(6.2)
Repurchase of common stock		(12.5)	(28.6)
Cash dividends and dividend equivalents paid		(21.9)	(20.1)
Net cash provided by (used in) financing activities		304.4	(55.5)
Net increase (decrease) in cash, cash equivalents and restricted cash during the period		446	(2.7)
Cash, cash equivalents and restricted cash at beginning of period		278.6	139.6
Cash, cash equivalents and restricted cash at end of period		$ 724.6	$ 136.9
[1]	See Note 13 for supplemental cash flow information.

Basis of Presentation, Economic

Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements	1. Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements This Quarterly Report on Form 10-Q (this "Report") should be read in conjunction with the Company's Annual Report on Form 10-K for the year ended December 31, 2019. Unless the context otherwise requires, references in these notes to interim consolidated financial statements - unaudited to "Kaiser Aluminum Corporation," "we," "us," "our," "the Company" and "our Company" refer collectively to Kaiser Aluminum Corporation and its subsidiaries. Principles of Consolidation and Basis of Presentation. The accompanying unaudited consolidated financial statements include the accounts of our wholly owned subsidiaries and are prepared in accordance with United States generally accepted accounting principles ("GAAP") and the rules and regulations of the Securities and Exchange Commission ("SEC") applicable for interim periods and, therefore, do not include all information and footnotes required by GAAP for complete financial statements. In management's opinion, all adjustments (which include normal recurring adjustments) considered necessary for a fair presentation have been included. The results of operations for our interim periods are not necessarily indicative of the results of operations that may be achieved for the entire 2020 fiscal year. The financial information as of December 31, 2019 is derived from our audited consolidated financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2019. Coronavirus Disease 2019 ( " " Beginning in March 2020, the COVID-19 pandemic significantly impacted our industry, causing demand for our products, primarily in our aerospace and automotive end markets, to decline. We instituted operational measures in response to financial impacts caused by the reduced demand. In March 2020, we suspended repurchases of our common stock. During the quarter ended June 30, 2020, we: (i) began limiting capital spending to critical sustaining projects (see Note 2 for discussion of idled projects); (ii) early settled firm commitments with corresponding fair value hedges and reduced forecasts with respect to purchase transactions with corresponding cash flow hedges (see Note 5); (iii) settled all outstanding available for sale securities (see Note 5); (iv) issued $350.0 million of new unsecured senior notes (see Note 6); and (v) initiated a plan of restructuring (see Note 9). For additional discussion related to the COVID-19 pandemic, see Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operations and Item 1A. Risk Factors, both of which are included in this Report. Use of Estimates in the Preparation of Financial Statements. The preparation of financial statements in accordance with GAAP requires the use of estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities known to exist as of the date the financial statements are published and the reported amounts of revenues and expenses during the reporting period. Uncertainties with respect to such estimates and assumptions are inherent in the preparation of our consolidated financial statements; accordingly, it is possible that the actual results could differ from these estimates and assumptions, which could have a material effect on the reported amounts of our consolidated financial position and results of operations. The severity, magnitude and duration, as well as the economic consequences of the COVID-19 pandemic, are uncertain, rapidly changing and difficult to predict. Therefore, our accounting estimates and assumptions may change over time in response to the COVID-19 pandemic and may change materially in future periods. Adoption of New Accounting Pronouncements Accounting Standards Update ("ASU") No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ASU No. 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract Accounting Pronouncements Issued But Not Yet Adopted ASU No. 2019-12, Simplifying the Accounting for Income Taxes Income Taxes

Supplemental Balance Sheet Info

Supplemental Balance Sheet Information	6 Months Ended
	Jun. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Supplemental Balance Sheet Information	2. Supplemental Balance Sheet Information June 30, 2020 December 31, 2019 (In millions of dollars) Cash and Cash Equivalents Cash and money market funds $ 710.6 $ 28.2 Commercial paper — 236.1 Total $ 710.6 $ 264.3 Trade Receivables, Net Billed trade receivables $ 127.5 $ 168.5 Allowance for doubtful receivables (1.1 ) (1.4 ) Trade receivables, net $ 126.4 $ 167.1 Inventories 1 Finished products $ 40.8 $ 42.6 Work-in-process 62.7 63.5 Raw materials 71.3 65.0 Operating supplies 6.6 6.5 Total $ 181.4 $ 177.6 Property, Plant and Equipment, Net Land and improvements $ 21.6 $ 21.4 Buildings and leasehold improvements 110.2 104.5 Machinery and equipment 826.9 813.5 Construction in progress 2 42.0 33.2 Property, plant and equipment, gross 1,000.7 972.6 Accumulated depreciation (375.1 ) (352.2 ) Assets held for sale 1.5 1.6 Property, plant and equipment, net $ 627.1 $ 622.0 Other Accrued Liabilities Uncleared cash disbursements $ 3.3 $ 4.2 Accrued income taxes and taxes payable 8.4 6.2 Accrued annual contribution to Salaried VEBA — 2.9 Accrued interest 11.8 2.3 Short-term environmental accrual – Note 7 6.6 5.5 Other – Note 3 and Note 5 24.4 22.9 Total $ 54.5 $ 44.0 Long-Term Liabilities Workers' compensation accrual 3 $ 29.6 $ 27.7 Long-term environmental accrual – Note 7 11.6 11.5 Other long-term liabilities 34.1 27.8 Total $ 75.3 $ 67.0 1 2 3

Leases

Leases	6 Months Ended
	Jun. 30, 2020
Leases [Abstract]
Leases	Leases We determine whether an agreement is a lease at inception. We have operating and finance leases for equipment and real estate that primarily have fixed lease payments. Our leases have remaining lease terms of approximately one to 13 years, some of which may include options to extend the lease for up to 20 years, and some of which may include options to terminate the lease within one year. None of our options to extend or terminate are reasonably certain of being exercised, and are therefore not included in our determination of lease assets and liabilities. Short-term leases with an initial term of 12 months or less are not recorded on our Consolidated Balance Sheets. As most of our leases do not provide an implicit rate, we use information available at the lease commencement date in determining an incremental borrowing rate when calculating our operating lease assets and operating lease liabilities. In determining the inputs to the incremental borrowing rate calculation, we make judgments about the value of the leased asset, our credit rating and the lease term, including the probability of our exercising options to extend or terminate the underlying lease. Additionally, we make judgments around contractual asset substitution rights in determining whether a contract contains a lease. We have lease agreements with lease and non-lease components, which are generally accounted for separately. These non-lease components include items such as common area maintenance, taxes and insurance for our real estate leases, as well as maintenance charges related to our equipment leases. We have, however, applied the practical expedient within ASU 2016-02 to not separate lease and non-lease components to our embedded supply system equipment leases and have therefore accounted for both lease and non-lease components in determining the lease assets and liabilities. Many of our equipment leases contain clauses that require us to return the equipment with certain functionality intact. We account for these costs as residual value guarantees when the guarantee becomes probable of being owed. Our lease agreements do not contain any material restrictive covenants. The following table presents lease terms and discount rates as of June 30, 2020: Finance Leases Operating Leases Weighted-average lease term (in years) 5.5 9.5 Weighted-average discount rate 4.6 % 5.4 % The following table summarizes the classification of lease assets and lease liabilities on our Consolidated Balance Sheets as of the periods presented (in millions of dollars): Leases Classification June 30, 2020 December 31, 2019 Assets Operating lease assets Operating lease assets $ 28.0 $ 25.8 Finance lease assets Property, plant and equipment, net 6.1 6.6 Total lease assets $ 34.1 $ 32.4 Liabilities Current: Operating lease liabilities Other accrued liabilities $ 4.5 $ 3.9 Finance lease liabilities Other accrued liabilities 1.3 1.2 Non-current: Operating lease liabilities Long-term portion of operating lease liabilities 27.0 25.2 Finance lease liabilities Long-term liabilities 4.8 5.4 Total lease liabilities $ 37.6 $ 35.7 The following table summarizes the components of lease cost on our Statements of Consolidated (Loss) Income for the periods presented (in millions of dollars): Quarter Ended Six Months Ended June 30, June 30, Lease Cost 2020 2019 2020 2019 Operating lease cost $ 1.8 $ 1.8 $ 3.6 $ 3.8 Short-term lease cost 0.3 0.2 0.6 0.5 Finance lease cost: Amortization of leased assets 0.3 0.3 0.7 0.7 Interest on lease liabilities 0.1 0.1 0.2 0.2 Total lease cost $ 2.5 $ 2.4 $ 5.1 $ 5.2 The following table presents the maturity of our lease liabilities as of June 30, 2020 (in millions of dollars): Maturity of Lease Liabilities Finance Leases Operating Leases Remainder of 2020 $ 0.8 $ 3.1 2021 1.5 5.6 2022 1.2 4.8 2023 1.1 4.4 2024 0.7 4.1 2025 0.7 2.3 2026 and thereafter 0.9 16.9 Total minimum lease payments $ 6.9 $ 41.2 Less: interest (0.8 ) (9.7 ) Present value $ 6.1 $ 31.5
Leases	Leases We determine whether an agreement is a lease at inception. We have operating and finance leases for equipment and real estate that primarily have fixed lease payments. Our leases have remaining lease terms of approximately one to 13 years, some of which may include options to extend the lease for up to 20 years, and some of which may include options to terminate the lease within one year. None of our options to extend or terminate are reasonably certain of being exercised, and are therefore not included in our determination of lease assets and liabilities. Short-term leases with an initial term of 12 months or less are not recorded on our Consolidated Balance Sheets. As most of our leases do not provide an implicit rate, we use information available at the lease commencement date in determining an incremental borrowing rate when calculating our operating lease assets and operating lease liabilities. In determining the inputs to the incremental borrowing rate calculation, we make judgments about the value of the leased asset, our credit rating and the lease term, including the probability of our exercising options to extend or terminate the underlying lease. Additionally, we make judgments around contractual asset substitution rights in determining whether a contract contains a lease. We have lease agreements with lease and non-lease components, which are generally accounted for separately. These non-lease components include items such as common area maintenance, taxes and insurance for our real estate leases, as well as maintenance charges related to our equipment leases. We have, however, applied the practical expedient within ASU 2016-02 to not separate lease and non-lease components to our embedded supply system equipment leases and have therefore accounted for both lease and non-lease components in determining the lease assets and liabilities. Many of our equipment leases contain clauses that require us to return the equipment with certain functionality intact. We account for these costs as residual value guarantees when the guarantee becomes probable of being owed. Our lease agreements do not contain any material restrictive covenants. The following table presents lease terms and discount rates as of June 30, 2020: Finance Leases Operating Leases Weighted-average lease term (in years) 5.5 9.5 Weighted-average discount rate 4.6 % 5.4 % The following table summarizes the classification of lease assets and lease liabilities on our Consolidated Balance Sheets as of the periods presented (in millions of dollars): Leases Classification June 30, 2020 December 31, 2019 Assets Operating lease assets Operating lease assets $ 28.0 $ 25.8 Finance lease assets Property, plant and equipment, net 6.1 6.6 Total lease assets $ 34.1 $ 32.4 Liabilities Current: Operating lease liabilities Other accrued liabilities $ 4.5 $ 3.9 Finance lease liabilities Other accrued liabilities 1.3 1.2 Non-current: Operating lease liabilities Long-term portion of operating lease liabilities 27.0 25.2 Finance lease liabilities Long-term liabilities 4.8 5.4 Total lease liabilities $ 37.6 $ 35.7 The following table summarizes the components of lease cost on our Statements of Consolidated (Loss) Income for the periods presented (in millions of dollars): Quarter Ended Six Months Ended June 30, June 30, Lease Cost 2020 2019 2020 2019 Operating lease cost $ 1.8 $ 1.8 $ 3.6 $ 3.8 Short-term lease cost 0.3 0.2 0.6 0.5 Finance lease cost: Amortization of leased assets 0.3 0.3 0.7 0.7 Interest on lease liabilities 0.1 0.1 0.2 0.2 Total lease cost $ 2.5 $ 2.4 $ 5.1 $ 5.2 The following table presents the maturity of our lease liabilities as of June 30, 2020 (in millions of dollars): Maturity of Lease Liabilities Finance Leases Operating Leases Remainder of 2020 $ 0.8 $ 3.1 2021 1.5 5.6 2022 1.2 4.8 2023 1.1 4.4 2024 0.7 4.1 2025 0.7 2.3 2026 and thereafter 0.9 16.9 Total minimum lease payments $ 6.9 $ 41.2 Less: interest (0.8 ) (9.7 ) Present value $ 6.1 $ 31.5

Employee Benefits

Employee Benefits	6 Months Ended
	Jun. 30, 2020
Compensation And Retirement Disclosure [Abstract]
Employee Benefits	4. Employee Benefits Short-Term Incentive Plans ("STI Plans"). We have annual short-term incentive compensation plans for senior management and certain other employees payable at our election in cash, shares of common stock or a combination of cash and shares of common stock. Amounts earned under STI Plans are based on our adjusted earnings before interest, taxes, depreciation and amortization ("Adjusted EBITDA"), modified for certain safety, quality, delivery, cost and individual performance factors. The Adjusted EBITDA targets are determined based on the return on adjusted net assets. Most of our production facilities have similar programs for both hourly and salaried employees. As of June 30, 2020, we had a liability of $3.5 million recorded within Accrued salaries, wages and related expenses for estimated probable future payments relating to the six month performance period of our 2020 STI Plan. Pension and Similar Benefit Plans. We provide contributions to: (i) defined contribution 401(k) savings plans for salaried employees and certain hourly employees; (ii) a non-qualified, unfunded, unsecured plan of deferred compensation (see " " below); (iii) multi-employer pension plans sponsored by the United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union, AFL-CIO, CLC, the International Association of Machinists and certain other unions at certain of our production facilities; and (iv) a defined benefit pension plan for salaried employees at our London, Ontario (Canada) facility. Deferred Compensation Plan . We have a non-qualified, unfunded, unsecured plan of deferred compensation for certain employees who would otherwise suffer a loss of benefits under our defined contribution plan as a result of the limitations imposed by the Internal Revenue Code of 1986. Despite the plan being an unfunded plan, we make an annual contribution to a rabbi trust to fulfill future funding obligations as contemplated by the terms of the plan. The assets in the trust are held in various investment funds at certain registered investment companies and are accounted for as equity investments with changes in fair value recorded within Other income (expense), net (see Note 10). Assets of our deferred compensation plan are included in Other assets, classified within Level 2 of the fair value hierarchy and are measured and recorded at fair value based on their quoted market prices. The fair value of these assets at June 30, 2020 and December 31, 2019 was $8.8 million and $8.1 million, respectively. Offsetting liabilities relating to the deferred compensation plan are included in Other accrued liabilities and Long-term liabilities. Salaried VEBA Postretirement Obligation. Certain retirees who retired prior to 2004 and certain employees who were hired prior to February 2002 and have subsequently retired or will retire with the requisite age and service, along with their surviving spouses and eligible dependents, are eligible to participate in a voluntary employees' beneficiary association ("VEBA") that provides healthcare cost, medical cost and long-term care insurance cost reimbursement benefits ("Salaried VEBA"). We have an ongoing obligation with no express termination date to make annual variable cash contributions up to a maximum of $2.9 million to the Salaried VEBA. We paid $2.9 million with respect to 2019 during the quarter ended March 31, 2020. We account for the Salaried VEBA as a defined benefit plan in our financial statements. The following table presents the total expense related to all postretirement benefit plans for the periods presented (in millions of dollars): Quarter Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Defined contribution plans 1 $ 1.7 $ 1.7 $ 5.6 $ 5.6 Deferred compensation plan 1 0.8 0.3 0.4 1.0 Multiemployer pension plans 1 1.2 1.2 2.5 2.4 Net periodic postretirement benefit cost relating to Salaried VEBA 2 1.2 1.6 2.4 3.3 Total $ 4.9 $ 4.8 $ 10.9 $ 12.3 1 2 Components of Net Periodic Benefit Cost. Our results of operations included the following impacts associated with our Canadian pension plan and the Salaried VEBA: (i) a charge for service rendered by employees; (ii) a charge for accretion of interest; (iii) a benefit for the expected return on plan assets; (iv) amortization of prior service costs associated with plan amendments; and (v) amortization of net actuarial differences. Net periodic benefit cost related to our Canadian pension plan was not material for the quarters and six months ended June 30, 2020 and June 30, 2019. The following table presents the components of Net periodic postretirement benefit cost relating to Salaried VEBA for the periods presented (in millions of dollars): Quarter Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Salaried VEBA 1 Interest cost $ 0.7 $ 0.8 $ 1.3 $ 1.6 Expected return on plan assets (0.7 ) (0.7 ) (1.4 ) (1.3 ) Amortization of prior service cost 2 1.1 1.4 2.3 2.8 Amortization of net actuarial loss 0.1 0.1 0.2 0.2 Total net periodic postretirement benefit cost relating to Salaried VEBA $ 1.2 $ 1.6 $ 2.4 $ 3.3 1 2

Derivatives, Hedging Programs a

Derivatives, Hedging Programs and Other Financial Instruments	6 Months Ended
	Jun. 30, 2020
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivatives, Hedging Programs and Other Financial Instruments	5. Derivatives, Hedging Programs and Other Financial Instruments Overview. In conducting our business, we enter into derivative transactions, including forward contracts and options, to limit our exposure to: (i) metal price risk related to our sale of fabricated aluminum products and the purchase of metal used as raw material for our fabrication operations; (ii) energy price risk relating to fluctuating prices of natural gas and electricity used in our production processes; and (iii) foreign currency requirements with respect to cash commitments for equipment purchases denominated in foreign currency. We do not use derivative financial instruments for trading or other speculative purposes. Hedging transactions are executed centrally on behalf of all of our operations to minimize transaction costs, monitor consolidated net exposures and allow for increased responsiveness to changes in market factors. Our derivative activities are overseen by a committee ("Hedging Committee"), which is composed of our chief executive officer, chief operating officer, chief financial officer, chief accounting officer, vice president of metal management, treasurer and other officers and employees selected by the chief executive officer. We are exposed to counterparty credit risk on all of our derivative instruments, which we manage by monitoring the credit quality of our counterparties and allocating our hedging positions among multiple counterparties to limit exposure to any single entity. Our counterparties are major, investment grade financial institutions or trading companies. Hedging transactions are governed by negotiated reciprocal credit lines, which generally require collateral to be posted above specified credit thresholds. We believe the risk of loss is remote and contained due to counterparty credit quality, our diversification practice and collateral requirements. In a majority of our hedging counterparty agreements, our counterparty offers us a credit line that adjusts up or down, depending on our liquidity. Below specified liquidity thresholds, we may have to post collateral if the fair value of our net liability with such counterparty exceeds our reduced credit line. We manage this risk by allocating hedging transactions among multiple counterparties, using options as part of our hedging activities or both. The aggregate fair value of our derivative instruments that were in a net liability position was $14.4 million and $7.2 million at June 30, 2020 and December 31, 2019, respectively, and we had no collateral posted as of those dates. Additionally, our firm-price customer sales commitments create incremental customer credit risk related to metal price movements. Under certain circumstances, we mitigate this risk by periodically requiring cash collateral from them, which we classify as deferred revenue and include as a component of Other accrued liabilities. Cash collateral posted from our customers was $0.5 million Cash Flow Hedges We designate our aluminum and energy derivatives and our forward swap contracts for zinc and copper ("Alloying Metals") used in our fabrication operations as cash flow hedges. Unrealized gains and losses associated with our cash flow hedges are deferred in Other comprehensive Aluminum Hedges . Our pricing of fabricated aluminum products is generally intended to lock in a conversion margin (representing the value added from the fabrication process(es)) and to pass through metal price fluctuations to our customers. For some of our higher value added products sold on a spot basis, the pass through of metal price movements can sometimes lag by as much as several months, with a favorable impact to us when metal prices decline and an adverse impact to us when metal prices increase. Additionally, in certain instances, we enter into firm-price arrangements with our customers for stipulated volumes to be delivered in the future. Because we generally purchase primary and secondary aluminum on a floating price basis, the lag in passing through metal price movements to customers on some of our higher value added products sold on a spot basis and the volume that we have committed to sell to our customers under a firm-price arrangement create metal price risk for us. We use third-party hedging instruments to limit exposure to metal price risk related to the metal pass through lag on some of our products and firm-price customer sales contracts. Alloying Metals Hedges . We are exposed to risk of fluctuating prices for Alloying Metals used as raw materials in our fabrication operations. We, from time to time, in the ordinary course of business, use third-party hedging instruments to mitigate our risk from price fluctuations in Alloying Metals. Energy Hedges . We are exposed to risk of fluctuating prices for natural gas and electricity. We, from time to time, in the ordinary course of business, enter into hedging transactions and/or physical delivery commitments with third parties to mitigate our risk from fluctuations in natural gas and electricity prices. Fair Value Hedges We are exposed to foreign currency exchange risk related to firm-price commitments for equipment purchases from foreign manufacturers. We, from time to time, in the ordinary course of business, use third-party hedging instruments to mitigate our exposure to currency exchange rate fluctuations on these purchases, and designate such hedging instruments as fair value hedges. Gain or loss related to components excluded from the assessment of effectiveness from these fair value hedges is first recognized in AOCI and subsequently reclassified to Depreciation and amortization on a straight-line basis over the term of the hedge. Gain or loss on the hedged item (e.g., equipment purchase firm commitments) and the remaining gain or loss on the fair value hedge is recorded within Depreciation and amortization in the period that the gain or loss occurs. Any difference between the change in the fair value of the excluded component and amounts recognized in income on a straight-line basis over the term of the hedge is recognized in AOCI. Non-Designated Hedges of Operational Risks From time-to-time, we enter into commodity and foreign currency exchange contracts that are not designated as hedging instruments to mitigate certain short-term commodity and currency impacts, as identified. For derivative instruments that are not designated as hedging instruments, the gain or loss on these derivatives is recognized within COGS or Other income (expense), net, depending on whether it relates to commodity risk or foreign currency risk, respectively. Notional Amount of Derivative Contracts The following table summarizes our derivative positions at June 30, 2020: Aluminum Maturity Period (month/year) Notional Amount of Contracts (mmlbs) Fixed price purchase contracts 7/20 through 12/22 92.4 Fixed price sales contracts 7/20 through 11/21 0.9 Midwest premium swap contracts 1 7/20 through 12/22 91.5 Alloying Metals Maturity Period (month/year) Notional Amount of Contracts (mmlbs) Fixed price purchase contracts 7/20 through 12/21 14.5 Fixed price sales contracts 7/20 through 12/21 5.8 Natural Gas 2 Maturity Period (month/year) Notional Amount of Contracts (mmbtu) Fixed price purchase contracts 7/20 through 12/24 7,490,000 Electricity 3 Maturity Period (month/year) Notional Amount of Contracts (Mwh) Fixed price purchase contracts 7/20 through 12/22 570,140 Euro Maturity Period (month/year) Notional Amount of Contracts (euro) Fixed price forward contracts 9/20 through 1/21 711,324 1 2 3 Loss (Gain) The amount of loss (gain) included on our Statements of Consolidated (Loss) Income associated with all derivative contracts consisted of the following for the periods presented (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Total of income and expense line items presented in our Statements of Consolidated (Loss) Income in which the effects of cash flow hedges are recorded $ 224.5 $ 303.5 $ 511.1 $ 618.6 Loss Aluminum 7.6 4.5 13.3 8.7 Alloying metals (effective hedges) 1.5 0.1 2.1 0.2 Alloying metals (reclassification due to forecasted transactions no longer probable of occurring) 0.7 — 0.7 — Natural gas 0.4 0.1 0.9 — Electricity 0.3 — 0.5 — Total loss recognized in our Statements of Consolidated (Loss) Income related to cash flow hedges $ 10.5 $ 4.7 $ 17.5 $ 8.9 Total of income and expense line items presented in our Statements of Consolidated (Loss) Income in which the effects of fair value hedges are recorded $ 13.0 $ 12.1 $ 26.2 $ 24.0 (Gain) loss recognized in our Statements of Consolidated (Loss) Income related to fair value hedges: Foreign exchange contracts (0.2 ) — — — Hedged item 0.2 — — — Excluded component amortized from AOCI 1 0.2 — 0.4 — Reclassification from AOCI related to early termination of firm commitment 1 (0.4 ) — (0.4 ) — Net settlement related to early termination of forward contracts 0.3 — 0.3 — Total gain recognized in our Statements of Consolidated (Loss) Income related to fair value hedges $ 0.1 $ — $ 0.3 $ — 1 Fair Values of D erivative Contracts The fair values of our derivative contracts are based upon trades in liquid markets. Valuation model inputs can be verified and valuation techniques do not involve significant judgment. The fair values of such financial instruments are classified within Level 2 of the fair value hierarchy. All of our derivative contracts with counterparties are subject to enforceable master netting arrangements. We reflect the fair value of our derivative contracts on a gross basis on our Consolidated Balance Sheets. The following table presents the fair value of our derivative financial instruments as of the periods presented (in millions of dollars): June 30, 2020 December 31, 2019 Assets Liabilities Net Amount Assets Liabilities Net Amount Cash Flow Hedges: Aluminum – Fixed price purchase contracts $ 0.3 $ (6.7 ) $ (6.4 ) $ 1.0 $ (4.1 ) $ (3.1 ) Fixed price sales contracts 0.1 — 0.1 — — — Midwest premium swap contracts 0.1 (2.7 ) (2.6 ) — (1.2 ) (1.2 ) Alloying Metals – Fixed price purchase contracts 0.2 (1.7 ) (1.5 ) 0.4 (1.5 ) (1.1 ) Natural gas – Fixed price purchase contracts 0.2 (2.7 ) (2.5 ) — (2.8 ) (2.8 ) Electricity – Fixed price purchase contracts 1.1 (2.6 ) (1.5 ) 2.6 (1.6 ) 1.0 Total $ 2.0 $ (16.4 ) $ (14.4 ) $ 4.0 $ (11.2 ) $ (7.2 ) The following table presents the total amounts of derivative assets and liabilities on our Consolidated Balance Sheets as of the periods presented (in millions of dollars): June 30, 2020 December 31, 2019 Derivative assets: Prepaid expenses and other current assets $ 1.2 $ 2.1 Other assets 0.8 1.9 Total derivative assets $ 2.0 $ 4.0 Derivative liabilities: Other accrued liabilities $ (9.8 ) $ (7.6 ) Long-term liabilities (6.6 ) (3.6 ) Total derivative liabilities $ (16.4 ) $ (11.2 ) Fair Value of Other Financial Instruments Cash and Cash Equivalents. See Note 2 for components of cash and cash equivalents. Available for Sale Securities . Prior to June 30, 2020, we held commercial paper debt securities that were accounted for as available for sale securities and presented as either cash equivalents or short-term investments on our Consolidated Balance Sheets depending on their time-to-maturity upon initial investment. At December 31, 2019, the fair value input of our available for sale securities, which were classified within Level 2 of the fair value hierarchy, was calculated based on broker quotes. The amortized cost of available for sale securities approximated their fair value. When applicable, we review our debt investment portfolio for credit loss at least quarterly or when there are changes in credit risk or other potential valuation concerns. Based on market conditions during the quarter ended June 30, 2020, we settled all remaining outstanding available for sale securities upon maturity. The following table classifies our other financial assets under the appropriate level of the fair value hierarchy as of June 30, 2020 (in millions of dollars): Level 1 Level 2 Level 3 Total Cash and cash equivalents $ 710.6 $ — $ — $ 710.6 Total $ 710.6 $ — $ — $ 710.6 The following table classifies our other financial assets under the appropriate level of the fair value hierarchy as of December 31, 2019 (in millions of dollars): Level 1 Level 2 Level 3 Total Cash and cash equivalents $ 28.2 $ 236.1 $ — $ 264.3 Short-term investments — 78.7 — 78.7 Total $ 28.2 $ 314.8 $ — $ 343.0 All Other Financial Assets and Liabilities. We believe that the fair values of our accounts receivable, contract assets, accounts payable and accrued liabilities approximate their respective carrying values due to their short maturities and nominal credit risk.

Debt and Credit Facility

Debt and Credit Facility	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Debt and Credit Facility	6. Debt and Credit Facility Senior Notes 6.50% Senior Notes. In April 2020 and May 2020, we issued $300.0 million and $50.0 million, respectively, aggregate principal amounts of our 6.50% unsecured senior notes due May 1, 2025 at 100% and 101%, respectively, of the principal amounts ("6.50% Senior Notes"). The restrictions and covenants related to our 6.50% Senior Notes are similar to those governing our pre-existing 4.625% unsecured senior notes due March 1, 2028 ("4.625% Senior Notes"). The unamortized amount of debt issuance costs relating to the 6.50% Senior Notes as of June 30, 2020 was $5.9 million. Interest expense, including amortization of debt issuance costs and debt premium, relating to the 6.50% Senior Notes was $4.2 million The 6.50% Senior Notes were offered and sold in transactions not required to be registered under the Securities Act of 1933 and are not entitled to any registration rights. The fair value of the outstanding 6.50% Senior Notes, which are Level 1 liabilities calculated based on pricing from trades around the balance sheet date, was approximately $365.5 million at June 30, 2020. The 6.50% Senior Notes are unsecured obligations and are guaranteed by each of our existing and future domestic subsidiaries that is a borrower or guarantor under the revolving credit facility (see Revolving Credit Facility We may redeem the 6.50% Senior Notes at our option in whole or part at any time on or after May 1, 2022 at redemption prices (expressed as percentages of principal amount) of 103.250%, declining to 101.625% and 100.000% on or after May 1, 2023 and May 1, 2024, respectively, in each case plus any accrued and unpaid interest to the applicable redemption date. At any time prior to May 1, 2022, we may also redeem up to 40.0% of the 6.50% Senior Notes using the net proceeds from certain equity offerings at a redemption price equal to 106.500% of the principal amount plus any accrued and unpaid interest. 4.625% Senior Notes. In November 2019, we issued $500.0 million principal amount of 4.625% unsecured senior notes due March 1, 2028 at 100% of the principal amount. The unamortized amount of debt issuance costs as of June 30, 2020 was $7.0 million . Interest expense, including amortization of debt issuance costs, relating to the 4.625% Senior Notes was $6.0 million and $12.0 million for the quarter and six months ended June 30, 2020, respectively. The effective interest rate of the 4.625% Senior Notes was approximately 4.8% per annum, taking into account the amortization of debt issuance costs. The fair value of the outstanding 4.625% Senior Notes, which are Level 1 liabilities, was approximately $482.2 million and $513.5 million at June 30, 2020 and December 31, 2019, respectively. 5.875% Senior Notes. In May 2016, we issued $375.0 million principal amount of 5.875% unsecured senior notes due May 15, 2024 ("5.875% Senior Notes") at 100% of the principal amount. On December 18, 2019, we redeemed in full all outstanding 5.875% Senior Notes at a redemption price of 104.406 % of the principal amount. The effective interest rate of the 5.875% Senior Notes was approximately 6.1 % per annum, taking into account the amortization of debt issuance costs. Interest expense, including amortization of debt issuance costs, relating to the 5.875% Senior Notes was $5.7 million and $11.4 million for the quarter and six months ended June 30, 2019 , respectively . The amount of interest expense capitalized as construction in progress was $0.2 million and $0.4 million during the quarters ended June 30, 2020 and June 30, 2019, respectively. The amount of interest expense capitalized as construction in progress was $0.5 million and $0.9 million during the six months ended June 30, 2020 and June 30, 2019, respectively. Revolving Credit Facility Our credit agreement with Wells Fargo Bank, National Association, as administrative agent, and the other financial institutions party thereto ("Revolving Credit Facility") provides us with a $375.0 million funding commitment through October 2024. The table below summarizes availability and usage of our Revolving Credit Facility as determined by a borrowing base calculated as of June 30, 2020 (in millions of dollars except for borrowing rate): Revolving Credit Facility borrowing commitment $ 375.0 Borrowing base availability $ 290.0 Less: Outstanding borrowings under Revolving Credit Facility — Less: Outstanding letters of credit under Revolving Credit Facility (7.7 ) Remaining borrowing availability $ 282.3 Borrowing rate (if applicable) 1 3.50 % 1

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Commitments. We have a variety of financial commitments, including purchase agreements, forward foreign exchange and forward sales contracts, indebtedness and letters of credit (see Note 5 and Note 6). Environmental Contingencies. We are subject to a number of environmental laws and regulations, to potential fines or penalties assessed for alleged breaches of such laws and regulations and to potential claims based upon such laws and regulations. We are also subject to legacy environmental contingencies related to activities that occurred at operating facilities prior to July 6, 2006, which represent the majority of our environmental accruals. The status of these environmental contingencies are discussed below. We have established procedures for regularly evaluating environmental loss contingencies. Our environmental accruals represent our undiscounted estimate of costs reasonably expected to be incurred based on presently enacted laws and regulations, existing requirements, currently available facts, existing technology and our assessment of the likely remediation actions to be taken. We continue to pursue remediation activities, primarily to address the historical use of oils containing polychlorinated biphenyls ("PCBs") at our Spokane, Washington ("Trentwood") facility. Our remediation efforts are in collaboration with the Washington State Department of Ecology ("Washington State Ecology"), to which we submitted a feasibility study in 2012 of remediation alternatives and from which we received permission to begin certain remediation activities pursuant to a signed work order. As we have finished a number of sections of the work plan, we have received approval from Washington State Ecology on satisfactory completion of those sections. Additionally, in cooperation with Washington State Ecology, to determine the treatability and evaluate the feasibility of removing PCBs from ground water under the Trentwood facility, we constructed an experimental treatment facility and began treatment operations in 2016. As the long-term success of the new methodology cannot be reasonably determined at this time, it is possible we may need to make upward adjustments to our related accruals and cost estimates as the long-term results become available. During 2013, at the request of the Ohio Environmental Protection Agency ("OEPA"), we initiated an investigational study of the Newark, Ohio ("Newark") facility related to historical on-site waste disposal. In the fourth quarter of 2018, we submitted our remedial investigation study to the OEPA, which is subject to their review and approval. Following OEPA approval of the remedial investigational study, we will then prepare the final feasibility study and update estimates for probable and estimable remediation, if any. The actual and final cost for remediation will not be fully determinable until a final feasibility study is submitted and accepted by the OEPA and work plans are prepared, which is expected to occur in the next 12 to 24 months. During 2020, following the issuance of information requests under the Comprehensive Environmental Response, Compensation and Liability Act of 1980 ("CERCLA"), to which we responded, United States Environmental Protection Agency ("USEPA") issued a general notice letter to us alleging that we are a potentially responsible party under CERCLA for response and other potential remedial actions concerning property owned by us near our former smelter site in Mead, Spokane County, Washington. On February 21, 2020, we responded to the General Notice letter and we continue to have discussions with USEPA regarding potential resolution of the matter. Final resolution is not yet certain, however, based on currently available facts and our assessment of the likely remediation actions to be taken, we established a $1.9 million short-term environmental accrual during the six months ended June 30, 2020. At June 30, 2020, our environmental accrual of $18.2 million represented our estimate of the incremental remediation cost based on: (i) proposed alternatives in the final feasibility study related to the Trentwood facility; (ii) currently available facts with respect to our Newark facility; and (iii) facts related to certain other locations owned or formerly owned by us, including our property in Mead, Spokane County, Washington. In accordance with approved and proposed remediation action plans, we expect that the implementation and ongoing monitoring could occur over a period of 30 or more years. As additional facts are developed, feasibility studies are completed, remediation plans are modified, necessary regulatory approvals for the implementation of remediation are obtained, alternative technologies are developed and/or other factors change, there may be revisions to management's estimates and actual costs may exceed the current environmental accruals. We believe at this time that it is reasonably possible that undiscounted costs associated with these environmental matters may exceed current accruals by amounts that could be, in the aggregate, up to an estimated $11.6 million over the remediation period. It is reasonably possible that our recorded estimate will change in the next 12 months. Other Contingencies. We are party to various lawsuits, claims, investigations and administrative proceedings that arise in connection with past and current operations. We evaluate such matters on a case-by-case basis and our policy is to vigorously contest any such claims we believe are without merit. We accrue for a legal liability when it is both probable that a liability has been incurred and the amount of the loss is reasonably estimable. Quarterly, in addition to when changes in facts and circumstances require it, we review and adjust these accruals to reflect the impacts of negotiations, settlements, rulings, advice of legal counsel and other information and events pertaining to a particular case. While uncertainties are inherent in the final outcome of such matters and it is presently impossible to determine the actual cost that may ultimately be incurred, we believe that we have sufficiently accrued for such matters and that the ultimate resolution of pending matters will not have a material impact on our consolidated financial position, operating results or liquidity.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Accumulated Other Comprehensive Loss	8. Accumulated Other Comprehensive Loss The following table presents the changes in the accumulated balances for each component of AOCI for the periods presented (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Defined Benefit Pension Plan and Salaried VEBA: Beginning balance $ (32.1 ) $ (34.5 ) $ (33.2 ) $ (35.6 ) Amortization of net actuarial loss 1 0.1 0.1 0.2 0.2 Amortization of prior service cost 1 1.1 1.4 2.3 2.8 Less: income tax expense 2 (0.3 ) (0.4 ) (0.6 ) (0.8 ) Net amortization reclassified from AOCI to Net (loss) income 0.9 1.1 1.9 2.2 Translation impact on Canadian pension plan AOCI balance — — 0.1 — Other comprehensive income, net of tax 0.9 1.1 2.0 2.2 Ending balance $ (31.2 ) $ (33.4 ) $ (31.2 ) $ (33.4 ) Available for Sale Securities: Beginning balance $ 0.1 $ 0.1 $ 0.3 $ 0.3 Unrealized gain on available for sale securities 0.1 0.7 1.4 1.7 Less: income tax expense — (0.1 ) (0.3 ) (0.4 ) Net unrealized gain on available for sale securities 0.1 0.6 1.1 1.3 Reclassification of unrealized gain upon sale of available for sale securities 3 (0.6 ) (0.9 ) (2.1 ) (2.1 ) Less: income tax benefit 2 0.2 0.2 0.5 0.5 Net gain reclassified from AOCI to Net (loss) income (0.4 ) (0.7 ) (1.6 ) (1.6 ) Other comprehensive loss, net of tax (0.3 ) (0.1 ) (0.5 ) (0.3 ) Ending balance $ (0.2 ) $ — $ (0.2 ) $ — Cash Flow Hedges: Beginning balance $ (21.5 ) $ (4.6 ) $ (5.6 ) $ (13.4 ) Unrealized gain (loss) on cash flow hedges 4.1 (10.1 ) (23.8 ) (2.7 ) Less: income tax (expense) benefit (0.9 ) 2.4 5.9 0.6 Net unrealized gain (loss) on cash flow hedges 3.2 (7.7 ) (17.9 ) (2.1 ) Reclassification of unrealized loss upon settlement of cash flow hedges 4 9.3 4.7 16.3 8.9 Reclassification due to forecasted sales no longer probable 4 0.7 — 0.7 — Less: income tax expense 2 (2.4 ) (1.2 ) (4.2 ) (2.2 ) Net loss reclassified from AOCI to Net (loss) income 7.6 3.5 12.8 6.7 Other comprehensive income (loss), net of tax 10.8 (4.2 ) (5.1 ) 4.6 Ending balance $ (10.7 ) $ (8.8 ) $ (10.7 ) $ (8.8 ) Fair Value Hedges: Beginning balance $ (0.5 ) $ — $ — $ — Unrealized gain (loss) on fair value hedges (0.2 ) — (1.0 ) — Less: income tax (expense) benefit — — 0.2 — Net unrealized gain (loss) on fair value hedges (0.2 ) — (0.8 ) — Excluded component amortized from OCI to Net (loss) income 5 0.2 — 0.4 — Reclassification due to cancellation of firm commitment 5 0.6 — 0.6 — Less: income tax expense 2 (0.1 ) — (0.2 ) — Net loss reclassified from AOCI to Net (loss) income 0.7 — 0.8 — Other comprehensive gain, net of tax 0.5 — — — Ending balance $ — $ — $ — $ — Foreign Currency Translation: Beginning balance $ (0.1 ) $ (0.1 ) $ (0.1 ) $ (0.1 ) Other comprehensive income, net of tax — — — — Ending balance $ (0.1 ) $ (0.1 ) $ (0.1 ) $ (0.1 ) Total AOCI ending balance $ (42.2 ) $ (42.3 ) $ (42.2 ) $ (42.3 ) 1 Amounts amortized out of AOCI relating to Salaried VEBA adjustments were included within Other income (expense) , net , as a component of Net periodic postretirement benefit cost relating to Salaried VEBA. 2 3 4 5

Restructuring

Restructuring	6 Months Ended
	Jun. 30, 2020
Restructuring And Related Activities [Abstract]
Restructuring	9. Restructuring During the quarter ended June 30, 2020, global restrictions on air travel and other changes in global travel patterns as a result of the Coronavirus Disease 2019 ("COVID-19") pandemic negatively impacted short and mid-term commercial aerospace demand within our Aero/HS products end market applications. We therefore initiated a restructuring plan that consisted of a reduction in force during the quarter ended June 30, 2020. Employee costs related to the reduction in force were included within Restructuring costs in our Statements of Consolidated (Loss) Income and consisted of severance, voluntary buyout packages, outplacement services, estimated medical costs and associated payroll costs The following table summarizes the activity relating to our restructuring plan liabilities (in millions of dollars): Six Months Ended June 30, 2020 Beginning balance $ — Restructuring costs 11.9 Cash payments (1.4 ) Ending balance $ 10.5

Other Income (Expense), Net

Other Income (Expense), Net	6 Months Ended
	Jun. 30, 2020
Other Income And Expenses [Abstract]
Other Income (Expense), Net	10. Other Income (Expense) Other income (expense) Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Interest income $ 0.2 $ 0.1 $ 0.3 $ 0.3 Net periodic postretirement benefit cost relating to Salaried VEBA (1.2 ) (1.6 ) (2.4 ) (3.3 ) Realized gain on available for sale securities 0.6 1.2 2.1 2.4 Unrealized gain on equity securities 0.7 — 0.1 0.5 All other income (expense), net 0.2 0.2 (0.4 ) 0.5 Other income (expense), net $ 0.5 $ (0.1 ) $ (0.3 ) $ 0.4

Income Tax Matters

Income Tax Matters	6 Months Ended
	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Income Tax Matters	11. Income Tax Matters The provision for in Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Domestic $ 1.0 $ 6.8 $ 10.6 $ 16.3 Foreign 0.3 0.5 0.3 0.8 Total $ 1.3 $ 7.3 $ 10.9 $ 17.1 The income tax provision for the quarters ended June 30, 2020 and June 30, 2019 was $1.3 24 an increase of $1.0 million (or 19% of taxable income) to the valuation allowance for certain state net operating losses and (ii) an increase of $1.9 million (or 37% of taxable income) for a change in forecasted earnings and its impact on the annual effective tax rate. The difference between the effective tax rate and the projected blended statutory tax rate for the quarter ended June 30, 2019 was primarily due to: (i) an increase of $0.5 million (2% of taxable income) related to non-deductible compensation expense and (ii) an increase of $0.2 million (1% of taxable income) related to unrecognized tax benefits, including interest and penalties. The income tax provision for the six months ended June 30, 2020 and June 30, 2019 was $10.9 million 33% (i) an increase of $0.8 million (or 2% of taxable income) related to non-deductible compensation expense; (ii) an increase of $1.3 million (or 4% of taxable income) to the valuation allowance for certain state net operating losses, partially offset by (i) a decrease of $0.6 million (or 2% of taxable income) for the recognition of excess tax benefits from stock-based compensation. The difference between the effective tax rate and the projected blended statutory tax rate for the six months ended June 30, 2019 was primarily due to: (i) an increase of $0.9 million (or 2% of taxable income) related to non-deductible compensation expense; (ii) an increase of $0.8 million (or 1% of taxable income) to the valuation allowance for certain state net operating losses, partially offset by (i) a decrease of $0.5 million (or 1% of taxable income) for the recognition of excess tax benefits from stock-based compensation. Our gross unrecognized benefits relating to uncertain tax positions were $3.9 million $0.4 million We do not expect our gross unrecognized tax benefits to significantly change within the next 12 months. On March 27, 2020, Congress enacted the Coronavirus Aid, Relief, and Economic Security ("CARES") Act to provide certain relief as a result of the COVID-19 pandemic. We are currently evaluating how provisions in the CARES Act will impact our consolidated financial statements.

Net (Loss) Income Per Share

Net (Loss) Income Per Share	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Net (Loss) Income Per Share	12. Net (Loss) Income Basic net (loss) income per share is computed by dividing distributed and undistributed net (loss) income allocable to common shares by the weighted-average number of common shares outstanding during the applicable period. The basic weighted-average number of common shares outstanding during the period excludes non-vested share-based payment awards. Diluted net (loss) income per share was calculated under the treasury stock method for the quarters and six months ended June 30, 2020 and June 30, 2019, which in both periods was more dilutive than the two-class method. The following table sets forth the computation of basic and diluted net (loss) income per share for the periods presented (in millions of dollars, except share and per share amounts): Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Numerator: Net (loss) income $ (6.6 ) $ 19.2 $ 22.5 $ 47.2 Denominator – Weighted-average common shares outstanding (in thousands): Basic 15,781 16,063 15,809 16,085 Add: dilutive effect of non-vested common shares, restricted stock units and performance shares 1 — 177 120 213 Diluted 15,781 16,240 15,929 16,298 Net (loss) income per common share, Basic: $ (0.41 ) $ 1.19 $ 1.42 $ 2.93 Net (loss) income per common share, Diluted: $ (0.41 ) $ 1.18 $ 1.41 $ 2.89 1 38,000

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	6 Months Ended
	Jun. 30, 2020
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	13. Supplemental Cash Flow Information Six Months Ended June 30, 2020 2019 (In millions of dollars) Interest paid $ 6.1 $ 10.7 Non-cash investing and financing activities (included in Accounts payable): Unpaid purchases of property and equipment $ 2.2 $ 2.4 Stock repurchases not yet settled $ — $ 0.3 Supplemental lease disclosures: Operating lease liabilities arising from obtaining operating lease assets $ 4.6 $ 0.9 Cash paid for amounts included in the measurement of operating lease liabilities $ 2.3 $ 1.8 Finance lease liabilities arising from obtaining finance lease assets $ 0.3 $ 0.5 June 30, 2020 June 30, 2019 (In millions of dollars) Components of cash, cash equivalents and restricted cash: Cash and cash equivalents $ 710.6 $ 122.4 Restricted cash included in Prepaid expenses and other current assets 1 — 0.3 Restricted cash included in Other assets 1 14.0 14.2 Total cash, cash equivalents and restricted cash presented on our Statements of Consolidated Cash Flows $ 724.6 $ 136.9 1

Business, Product and Geographi

Business, Product and Geographical Area Information	6 Months Ended
	Jun. 30, 2020
Segment Reporting [Abstract]
Business, Product and Geographical Area Information	14. Business, Product and Geographical Area Information Our primary line of business is the production of semi-fabricated specialty aluminum mill products, such as aluminum plate and sheet and extruded and drawn products, primarily used in aerospace and high strength ("Aero/HS products"), automotive ("Automotive Extrusions"), general engineering ("GE products") and other industrial ("Other products"). We operate 12 focused production facilities in the United States and one in Canada. Our chief operating decision maker reviews and evaluates our business as a single operating segment. The following table presents Net sales by end market applications and by timing of control transfer for the periods presented (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Net sales: Aero/HS products $ 144.6 $ 189.4 $ 340.6 $ 387.9 Automotive Extrusions 16.7 45.5 64.1 98.5 GE products 110.8 128.2 232.5 258.2 Other products 3.6 12.2 7.8 25.9 Total net sales $ 275.7 $ 375.3 $ 645.0 $ 770.5 Timing of revenue recognition: Products transferred at a point in time $ 164.7 $ 222.6 1 $ 380.3 $ 445.9 2 Products transferred over time 111.0 152.7 1 264.7 324.6 2 Total net sales $ 275.7 $ 375.3 $ 645.0 $ 770.5 1. 2. The following table presents geographic information for income taxes paid for the periods presented (in millions of dollars): Quarter Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Income taxes paid: Domestic $ 0.3 $ 1.8 $ 0.3 $ 1.9 Foreign — 0.4 0.1 1.2 Total income taxes paid $ 0.3 $ 2.2 $ 0.4 $ 3.1

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	15. Subsequent Events Dividend Declaration. On July 14, 2020, we announced that our Board of Directors declared a cash dividend of $0.67 per common share. As such, we expect to pay approximately $10.7 million (including dividend equivalents) on or about August 14, 2020 to stockholders of record and the holders of certain restricted stock units at the close of business on July 24, 2020.

Basis of Presentation, Econom_2

Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements (Policies)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Principles of Consolidation and Basis of Presentation	Principles of Consolidation and Basis of Presentation. The accompanying unaudited consolidated financial statements include the accounts of our wholly owned subsidiaries and are prepared in accordance with United States generally accepted accounting principles ("GAAP") and the rules and regulations of the Securities and Exchange Commission ("SEC") applicable for interim periods and, therefore, do not include all information and footnotes required by GAAP for complete financial statements. In management's opinion, all adjustments (which include normal recurring adjustments) considered necessary for a fair presentation have been included. The results of operations for our interim periods are not necessarily indicative of the results of operations that may be achieved for the entire 2020 fiscal year. The financial information as of December 31, 2019 is derived from our audited consolidated financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2019.
Coronavirus Disease 2019 ("COVID-19") Pandemic	Coronavirus Disease 2019 ( " " Beginning in March 2020, the COVID-19 pandemic significantly impacted our industry, causing demand for our products, primarily in our aerospace and automotive end markets, to decline. We instituted operational measures in response to financial impacts caused by the reduced demand. In March 2020, we suspended repurchases of our common stock. During the quarter ended June 30, 2020, we: (i) began limiting capital spending to critical sustaining projects (see Note 2 for discussion of idled projects); (ii) early settled firm commitments with corresponding fair value hedges and reduced forecasts with respect to purchase transactions with corresponding cash flow hedges (see Note 5); (iii) settled all outstanding available for sale securities (see Note 5); (iv) issued $350.0 million of new unsecured senior notes (see Note 6); and (v) initiated a plan of restructuring (see Note 9). For additional discussion related to the COVID-19 pandemic, see Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operations and Item 1A. Risk Factors, both of which are included in this Report.
Use of Estimates in the Preparation of Financial Statements	Use of Estimates in the Preparation of Financial Statements. The preparation of financial statements in accordance with GAAP requires the use of estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities known to exist as of the date the financial statements are published and the reported amounts of revenues and expenses during the reporting period. Uncertainties with respect to such estimates and assumptions are inherent in the preparation of our consolidated financial statements; accordingly, it is possible that the actual results could differ from these estimates and assumptions, which could have a material effect on the reported amounts of our consolidated financial position and results of operations. The severity, magnitude and duration, as well as the economic consequences of the COVID-19 pandemic, are uncertain, rapidly changing and difficult to predict. Therefore, our accounting estimates and assumptions may change over time in response to the COVID-19 pandemic and may change materially in future periods.
New Accounting Pronouncements	Adoption of New Accounting Pronouncements Accounting Standards Update ("ASU") No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ASU No. 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract Accounting Pronouncements Issued But Not Yet Adopted ASU No. 2019-12, Simplifying the Accounting for Income Taxes Income Taxes
Leases	We determine whether an agreement is a lease at inception. We have operating and finance leases for equipment and real estate that primarily have fixed lease payments. Our leases have remaining lease terms of approximately one to 13 years, some of which may include options to extend the lease for up to 20 years, and some of which may include options to terminate the lease within one year. None of our options to extend or terminate are reasonably certain of being exercised, and are therefore not included in our determination of lease assets and liabilities. Short-term leases with an initial term of 12 months or less are not recorded on our Consolidated Balance Sheets. As most of our leases do not provide an implicit rate, we use information available at the lease commencement date in determining an incremental borrowing rate when calculating our operating lease assets and operating lease liabilities. In determining the inputs to the incremental borrowing rate calculation, we make judgments about the value of the leased asset, our credit rating and the lease term, including the probability of our exercising options to extend or terminate the underlying lease. Additionally, we make judgments around contractual asset substitution rights in determining whether a contract contains a lease. We have lease agreements with lease and non-lease components, which are generally accounted for separately. These non-lease components include items such as common area maintenance, taxes and insurance for our real estate leases, as well as maintenance charges related to our equipment leases. We have, however, applied the practical expedient within ASU 2016-02 to not separate lease and non-lease components to our embedded supply system equipment leases and have therefore accounted for both lease and non-lease components in determining the lease assets and liabilities. Many of our equipment leases contain clauses that require us to return the equipment with certain functionality intact. We account for these costs as residual value guarantees when the guarantee becomes probable of being owed. Our lease agreements do not contain any material restrictive covenants.

Supplemental Balance Sheet In_2

Supplemental Balance Sheet Information (Tables)	6 Months Ended
	Jun. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Supplemental Balance Sheet Information	Supplemental Balance Sheet Information June 30, 2020 December 31, 2019 (In millions of dollars) Cash and Cash Equivalents Cash and money market funds $ 710.6 $ 28.2 Commercial paper — 236.1 Total $ 710.6 $ 264.3 Trade Receivables, Net Billed trade receivables $ 127.5 $ 168.5 Allowance for doubtful receivables (1.1 ) (1.4 ) Trade receivables, net $ 126.4 $ 167.1 Inventories 1 Finished products $ 40.8 $ 42.6 Work-in-process 62.7 63.5 Raw materials 71.3 65.0 Operating supplies 6.6 6.5 Total $ 181.4 $ 177.6 Property, Plant and Equipment, Net Land and improvements $ 21.6 $ 21.4 Buildings and leasehold improvements 110.2 104.5 Machinery and equipment 826.9 813.5 Construction in progress 2 42.0 33.2 Property, plant and equipment, gross 1,000.7 972.6 Accumulated depreciation (375.1 ) (352.2 ) Assets held for sale 1.5 1.6 Property, plant and equipment, net $ 627.1 $ 622.0 Other Accrued Liabilities Uncleared cash disbursements $ 3.3 $ 4.2 Accrued income taxes and taxes payable 8.4 6.2 Accrued annual contribution to Salaried VEBA — 2.9 Accrued interest 11.8 2.3 Short-term environmental accrual – Note 7 6.6 5.5 Other – Note 3 and Note 5 24.4 22.9 Total $ 54.5 $ 44.0 Long-Term Liabilities Workers' compensation accrual 3 $ 29.6 $ 27.7 Long-term environmental accrual – Note 7 11.6 11.5 Other long-term liabilities 34.1 27.8 Total $ 75.3 $ 67.0 1 2 3

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2020
Leases [Abstract]
Schedule of Lease Terms and Discount Rates	The following table presents lease terms and discount rates as of June 30, 2020: Finance Leases Operating Leases Weighted-average lease term (in years) 5.5 9.5 Weighted-average discount rate 4.6 % 5.4 %
Schedule of Lease Assets and Lease Liabilities	The following table summarizes the classification of lease assets and lease liabilities on our Consolidated Balance Sheets as of the periods presented (in millions of dollars): Leases Classification June 30, 2020 December 31, 2019 Assets Operating lease assets Operating lease assets $ 28.0 $ 25.8 Finance lease assets Property, plant and equipment, net 6.1 6.6 Total lease assets $ 34.1 $ 32.4 Liabilities Current: Operating lease liabilities Other accrued liabilities $ 4.5 $ 3.9 Finance lease liabilities Other accrued liabilities 1.3 1.2 Non-current: Operating lease liabilities Long-term portion of operating lease liabilities 27.0 25.2 Finance lease liabilities Long-term liabilities 4.8 5.4 Total lease liabilities $ 37.6 $ 35.7
Components of Lease Cost	The following table summarizes the components of lease cost on our Statements of Consolidated (Loss) Income for the periods presented (in millions of dollars): Quarter Ended Six Months Ended June 30, June 30, Lease Cost 2020 2019 2020 2019 Operating lease cost $ 1.8 $ 1.8 $ 3.6 $ 3.8 Short-term lease cost 0.3 0.2 0.6 0.5 Finance lease cost: Amortization of leased assets 0.3 0.3 0.7 0.7 Interest on lease liabilities 0.1 0.1 0.2 0.2 Total lease cost $ 2.5 $ 2.4 $ 5.1 $ 5.2
Schedule of Maturity of Our Lease Liabilities	The following table presents the maturity of our lease liabilities as of June 30, 2020 (in millions of dollars): Maturity of Lease Liabilities Finance Leases Operating Leases Remainder of 2020 $ 0.8 $ 3.1 2021 1.5 5.6 2022 1.2 4.8 2023 1.1 4.4 2024 0.7 4.1 2025 0.7 2.3 2026 and thereafter 0.9 16.9 Total minimum lease payments $ 6.9 $ 41.2 Less: interest (0.8 ) (9.7 ) Present value $ 6.1 $ 31.5

Employee Benefits (Tables)

Employee Benefits (Tables)	6 Months Ended
	Jun. 30, 2020
Compensation And Retirement Disclosure [Abstract]
Schedule of Total Expense Related to Benefit Plans	The following table presents the total expense related to all postretirement benefit plans for the periods presented (in millions of dollars): Quarter Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Defined contribution plans 1 $ 1.7 $ 1.7 $ 5.6 $ 5.6 Deferred compensation plan 1 0.8 0.3 0.4 1.0 Multiemployer pension plans 1 1.2 1.2 2.5 2.4 Net periodic postretirement benefit cost relating to Salaried VEBA 2 1.2 1.6 2.4 3.3 Total $ 4.9 $ 4.8 $ 10.9 $ 12.3 1 2
Schedule of Net Benefit Costs	The following table presents the components of Net periodic postretirement benefit cost relating to Salaried VEBA for the periods presented (in millions of dollars): Quarter Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Salaried VEBA 1 Interest cost $ 0.7 $ 0.8 $ 1.3 $ 1.6 Expected return on plan assets (0.7 ) (0.7 ) (1.4 ) (1.3 ) Amortization of prior service cost 2 1.1 1.4 2.3 2.8 Amortization of net actuarial loss 0.1 0.1 0.2 0.2 Total net periodic postretirement benefit cost relating to Salaried VEBA $ 1.2 $ 1.6 $ 2.4 $ 3.3 1 2

Derivatives, Hedging Programs_2

Derivatives, Hedging Programs and Other Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2020
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Summary of Derivative Positions	The following table summarizes our derivative positions at June 30, 2020: Aluminum Maturity Period (month/year) Notional Amount of Contracts (mmlbs) Fixed price purchase contracts 7/20 through 12/22 92.4 Fixed price sales contracts 7/20 through 11/21 0.9 Midwest premium swap contracts 1 7/20 through 12/22 91.5 Alloying Metals Maturity Period (month/year) Notional Amount of Contracts (mmlbs) Fixed price purchase contracts 7/20 through 12/21 14.5 Fixed price sales contracts 7/20 through 12/21 5.8 Natural Gas 2 Maturity Period (month/year) Notional Amount of Contracts (mmbtu) Fixed price purchase contracts 7/20 through 12/24 7,490,000 Electricity 3 Maturity Period (month/year) Notional Amount of Contracts (Mwh) Fixed price purchase contracts 7/20 through 12/22 570,140 Euro Maturity Period (month/year) Notional Amount of Contracts (euro) Fixed price forward contracts 9/20 through 1/21 711,324 1 2 3
Summary of Loss (Gain) Associated with Derivative Contracts	The amount of loss (gain) included on our Statements of Consolidated (Loss) Income associated with all derivative contracts consisted of the following for the periods presented (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Total of income and expense line items presented in our Statements of Consolidated (Loss) Income in which the effects of cash flow hedges are recorded $ 224.5 $ 303.5 $ 511.1 $ 618.6 Loss Aluminum 7.6 4.5 13.3 8.7 Alloying metals (effective hedges) 1.5 0.1 2.1 0.2 Alloying metals (reclassification due to forecasted transactions no longer probable of occurring) 0.7 — 0.7 — Natural gas 0.4 0.1 0.9 — Electricity 0.3 — 0.5 — Total loss recognized in our Statements of Consolidated (Loss) Income related to cash flow hedges $ 10.5 $ 4.7 $ 17.5 $ 8.9 Total of income and expense line items presented in our Statements of Consolidated (Loss) Income in which the effects of fair value hedges are recorded $ 13.0 $ 12.1 $ 26.2 $ 24.0 (Gain) loss recognized in our Statements of Consolidated (Loss) Income related to fair value hedges: Foreign exchange contracts (0.2 ) — — — Hedged item 0.2 — — — Excluded component amortized from AOCI 1 0.2 — 0.4 — Reclassification from AOCI related to early termination of firm commitment 1 (0.4 ) — (0.4 ) — Net settlement related to early termination of forward contracts 0.3 — 0.3 — Total gain recognized in our Statements of Consolidated (Loss) Income related to fair value hedges $ 0.1 $ — $ 0.3 $ —
Schedule of Fair Value of Derivative Financial Instruments	The following table presents the fair value of our derivative financial instruments as of the periods presented (in millions of dollars): June 30, 2020 December 31, 2019 Assets Liabilities Net Amount Assets Liabilities Net Amount Cash Flow Hedges: Aluminum – Fixed price purchase contracts $ 0.3 $ (6.7 ) $ (6.4 ) $ 1.0 $ (4.1 ) $ (3.1 ) Fixed price sales contracts 0.1 — 0.1 — — — Midwest premium swap contracts 0.1 (2.7 ) (2.6 ) — (1.2 ) (1.2 ) Alloying Metals – Fixed price purchase contracts 0.2 (1.7 ) (1.5 ) 0.4 (1.5 ) (1.1 ) Natural gas – Fixed price purchase contracts 0.2 (2.7 ) (2.5 ) — (2.8 ) (2.8 ) Electricity – Fixed price purchase contracts 1.1 (2.6 ) (1.5 ) 2.6 (1.6 ) 1.0 Total $ 2.0 $ (16.4 ) $ (14.4 ) $ 4.0 $ (11.2 ) $ (7.2 ) The following table presents the total amounts of derivative assets and liabilities on our Consolidated Balance Sheets as of the periods presented (in millions of dollars): June 30, 2020 December 31, 2019 Derivative assets: Prepaid expenses and other current assets $ 1.2 $ 2.1 Other assets 0.8 1.9 Total derivative assets $ 2.0 $ 4.0 Derivative liabilities: Other accrued liabilities $ (9.8 ) $ (7.6 ) Long-term liabilities (6.6 ) (3.6 ) Total derivative liabilities $ (16.4 ) $ (11.2 )
Schedule of Other Financial Assets Classifies under Appropriate Level of Fair Value Hierarchy	The following table classifies our other financial assets under the appropriate level of the fair value hierarchy as of June 30, 2020 (in millions of dollars): Level 1 Level 2 Level 3 Total Cash and cash equivalents $ 710.6 $ — $ — $ 710.6 Total $ 710.6 $ — $ — $ 710.6 The following table classifies our other financial assets under the appropriate level of the fair value hierarchy as of December 31, 2019 (in millions of dollars): Level 1 Level 2 Level 3 Total Cash and cash equivalents $ 28.2 $ 236.1 $ — $ 264.3 Short-term investments — 78.7 — 78.7 Total $ 28.2 $ 314.8 $ — $ 343.0

Debt and Credit Facility (Table

Debt and Credit Facility (Tables)	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Schedule of Availability and Usage of Revolving Credit Facility	The table below summarizes availability and usage of our Revolving Credit Facility as determined by a borrowing base calculated as of June 30, 2020 (in millions of dollars except for borrowing rate): Revolving Credit Facility borrowing commitment $ 375.0 Borrowing base availability $ 290.0 Less: Outstanding borrowings under Revolving Credit Facility — Less: Outstanding letters of credit under Revolving Credit Facility (7.7 ) Remaining borrowing availability $ 282.3 Borrowing rate (if applicable) 1 3.50 % 1

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss (Tables)	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following table presents the changes in the accumulated balances for each component of AOCI for the periods presented (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Defined Benefit Pension Plan and Salaried VEBA: Beginning balance $ (32.1 ) $ (34.5 ) $ (33.2 ) $ (35.6 ) Amortization of net actuarial loss 1 0.1 0.1 0.2 0.2 Amortization of prior service cost 1 1.1 1.4 2.3 2.8 Less: income tax expense 2 (0.3 ) (0.4 ) (0.6 ) (0.8 ) Net amortization reclassified from AOCI to Net (loss) income 0.9 1.1 1.9 2.2 Translation impact on Canadian pension plan AOCI balance — — 0.1 — Other comprehensive income, net of tax 0.9 1.1 2.0 2.2 Ending balance $ (31.2 ) $ (33.4 ) $ (31.2 ) $ (33.4 ) Available for Sale Securities: Beginning balance $ 0.1 $ 0.1 $ 0.3 $ 0.3 Unrealized gain on available for sale securities 0.1 0.7 1.4 1.7 Less: income tax expense — (0.1 ) (0.3 ) (0.4 ) Net unrealized gain on available for sale securities 0.1 0.6 1.1 1.3 Reclassification of unrealized gain upon sale of available for sale securities 3 (0.6 ) (0.9 ) (2.1 ) (2.1 ) Less: income tax benefit 2 0.2 0.2 0.5 0.5 Net gain reclassified from AOCI to Net (loss) income (0.4 ) (0.7 ) (1.6 ) (1.6 ) Other comprehensive loss, net of tax (0.3 ) (0.1 ) (0.5 ) (0.3 ) Ending balance $ (0.2 ) $ — $ (0.2 ) $ — Cash Flow Hedges: Beginning balance $ (21.5 ) $ (4.6 ) $ (5.6 ) $ (13.4 ) Unrealized gain (loss) on cash flow hedges 4.1 (10.1 ) (23.8 ) (2.7 ) Less: income tax (expense) benefit (0.9 ) 2.4 5.9 0.6 Net unrealized gain (loss) on cash flow hedges 3.2 (7.7 ) (17.9 ) (2.1 ) Reclassification of unrealized loss upon settlement of cash flow hedges 4 9.3 4.7 16.3 8.9 Reclassification due to forecasted sales no longer probable 4 0.7 — 0.7 — Less: income tax expense 2 (2.4 ) (1.2 ) (4.2 ) (2.2 ) Net loss reclassified from AOCI to Net (loss) income 7.6 3.5 12.8 6.7 Other comprehensive income (loss), net of tax 10.8 (4.2 ) (5.1 ) 4.6 Ending balance $ (10.7 ) $ (8.8 ) $ (10.7 ) $ (8.8 ) Fair Value Hedges: Beginning balance $ (0.5 ) $ — $ — $ — Unrealized gain (loss) on fair value hedges (0.2 ) — (1.0 ) — Less: income tax (expense) benefit — — 0.2 — Net unrealized gain (loss) on fair value hedges (0.2 ) — (0.8 ) — Excluded component amortized from OCI to Net (loss) income 5 0.2 — 0.4 — Reclassification due to cancellation of firm commitment 5 0.6 — 0.6 — Less: income tax expense 2 (0.1 ) — (0.2 ) — Net loss reclassified from AOCI to Net (loss) income 0.7 — 0.8 — Other comprehensive gain, net of tax 0.5 — — — Ending balance $ — $ — $ — $ — Foreign Currency Translation: Beginning balance $ (0.1 ) $ (0.1 ) $ (0.1 ) $ (0.1 ) Other comprehensive income, net of tax — — — — Ending balance $ (0.1 ) $ (0.1 ) $ (0.1 ) $ (0.1 ) Total AOCI ending balance $ (42.2 ) $ (42.3 ) $ (42.2 ) $ (42.3 ) 1 Amounts amortized out of AOCI relating to Salaried VEBA adjustments were included within Other income (expense) , net , as a component of Net periodic postretirement benefit cost relating to Salaried VEBA. 2 3 4 5

Restructuring (Tables)

Restructuring (Tables)	6 Months Ended
	Jun. 30, 2020
Restructuring And Related Activities [Abstract]
Summary of Activity Relating to Restructuring Plan Liabilities	The following table summarizes the activity relating to our restructuring plan liabilities (in millions of dollars): Six Months Ended June 30, 2020 Beginning balance $ — Restructuring costs 11.9 Cash payments (1.4 ) Ending balance $ 10.5

Other Income (Expense), Net (Ta

Other Income (Expense), Net (Tables)	6 Months Ended
	Jun. 30, 2020
Other Income And Expenses [Abstract]
Other Income (Expense), Net	Other income (expense) Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Interest income $ 0.2 $ 0.1 $ 0.3 $ 0.3 Net periodic postretirement benefit cost relating to Salaried VEBA (1.2 ) (1.6 ) (2.4 ) (3.3 ) Realized gain on available for sale securities 0.6 1.2 2.1 2.4 Unrealized gain on equity securities 0.7 — 0.1 0.5 All other income (expense), net 0.2 0.2 (0.4 ) 0.5 Other income (expense), net $ 0.5 $ (0.1 ) $ (0.3 ) $ 0.4

Income Tax Matters (Tables)

Income Tax Matters (Tables)	6 Months Ended
	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Schedule of Provision for Income Taxes	The provision for in Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Domestic $ 1.0 $ 6.8 $ 10.6 $ 16.3 Foreign 0.3 0.5 0.3 0.8 Total $ 1.3 $ 7.3 $ 10.9 $ 17.1

Net (Loss) Income Per Share (Ta

Net (Loss) Income Per Share (Tables)	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Schedule of Calculation of Basic and Diluted Net (Loss) Income Per Share	The following table sets forth the computation of basic and diluted net (loss) income per share for the periods presented (in millions of dollars, except share and per share amounts): Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Numerator: Net (loss) income $ (6.6 ) $ 19.2 $ 22.5 $ 47.2 Denominator – Weighted-average common shares outstanding (in thousands): Basic 15,781 16,063 15,809 16,085 Add: dilutive effect of non-vested common shares, restricted stock units and performance shares 1 — 177 120 213 Diluted 15,781 16,240 15,929 16,298 Net (loss) income per common share, Basic: $ (0.41 ) $ 1.19 $ 1.42 $ 2.93 Net (loss) income per common share, Diluted: $ (0.41 ) $ 1.18 $ 1.41 $ 2.89 1 38,000

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	6 Months Ended
	Jun. 30, 2020
Supplemental Cash Flow Elements [Abstract]
Schedule of Supplemental Cash Flow Information	Six Months Ended June 30, 2020 2019 (In millions of dollars) Interest paid $ 6.1 $ 10.7 Non-cash investing and financing activities (included in Accounts payable): Unpaid purchases of property and equipment $ 2.2 $ 2.4 Stock repurchases not yet settled $ — $ 0.3 Supplemental lease disclosures: Operating lease liabilities arising from obtaining operating lease assets $ 4.6 $ 0.9 Cash paid for amounts included in the measurement of operating lease liabilities $ 2.3 $ 1.8 Finance lease liabilities arising from obtaining finance lease assets $ 0.3 $ 0.5 June 30, 2020 June 30, 2019 (In millions of dollars) Components of cash, cash equivalents and restricted cash: Cash and cash equivalents $ 710.6 $ 122.4 Restricted cash included in Prepaid expenses and other current assets 1 — 0.3 Restricted cash included in Other assets 1 14.0 14.2 Total cash, cash equivalents and restricted cash presented on our Statements of Consolidated Cash Flows $ 724.6 $ 136.9 1

Business, Product and Geograp_2

Business, Product and Geographical Area Information (Tables)	6 Months Ended
	Jun. 30, 2020
Segment Reporting [Abstract]
Schedule of Net Sales by End Market Segment Applications	The following table presents Net sales by end market applications and by timing of control transfer for the periods presented (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Net sales: Aero/HS products $ 144.6 $ 189.4 $ 340.6 $ 387.9 Automotive Extrusions 16.7 45.5 64.1 98.5 GE products 110.8 128.2 232.5 258.2 Other products 3.6 12.2 7.8 25.9 Total net sales $ 275.7 $ 375.3 $ 645.0 $ 770.5 Timing of revenue recognition: Products transferred at a point in time $ 164.7 $ 222.6 1 $ 380.3 $ 445.9 2 Products transferred over time 111.0 152.7 1 264.7 324.6 2 Total net sales $ 275.7 $ 375.3 $ 645.0 $ 770.5 1. 2.
Schedule of Income Taxes Paid by Geographical Area	The following table presents geographic information for income taxes paid for the periods presented (in millions of dollars): Quarter Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Income taxes paid: Domestic $ 0.3 $ 1.8 $ 0.3 $ 1.9 Foreign — 0.4 0.1 1.2 Total income taxes paid $ 0.3 $ 2.2 $ 0.4 $ 3.1

Basis of Presentation, Econom_3

Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements - Additional Information (Details) - USD ($)	Jun. 30, 2020	May 01, 2020	Apr. 28, 2020
Senior Notes Due 2025 | Senior Notes
Significant Accounting Policies [Line Items]
Debt principal amount	$ 350,000,000	$ 50,000,000	$ 300,000,000

Supplemental Balance Sheet In_3

Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Cash and Cash Equivalents
Cash and money market funds	$ 710.6	$ 28.2
Commercial paper		236.1
Total	710.6	264.3
Trade Receivables, Net
Allowance for doubtful receivables	(1.1)	(1.4)
Trade receivables, net	126.4	167.1
Inventories
Finished products	40.8	42.6
Work-in-process	62.7	63.5
Raw materials	71.3	65
Operating supplies	6.6	6.5
Total	181.4	177.6
Property, Plant and Equipment, Net
Land and improvements	21.6	21.4
Buildings and leasehold improvements	110.2	104.5
Machinery and equipment	826.9	813.5
Construction in progress	42	33.2
Property, plant and equipment, gross	1,000.7	972.6
Accumulated depreciation	(375.1)	(352.2)
Assets held for sale	1.5	1.6
Property, plant and equipment, net	627.1	622
Other Accrued Liabilities
Uncleared cash disbursements	3.3	4.2
Accrued income taxes and taxes payable	8.4	6.2
Accrued annual contribution to Salaried VEBA		2.9
Accrued interest	11.8	2.3
Short-term environmental accrual	6.6	5.5
Other	24.4	22.9
Total	54.5	44
Long-Term Liabilities
Workers' compensation accrual	29.6	27.7
Long-term environmental accrual	11.6	11.5
Other long-term liabilities	34.1	27.8
Total	75.3	67
Billed
Trade Receivables, Net
Billed trade receivables	$ 127.5	$ 168.5

Supplemental Balance Sheet In_4

Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Parenthetical) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Excess of Replacement or Current Costs over Stated LIFO Value		$ 11.9
Excess of stated LIFO value over replacement or current costs	$ 11
Construction in progress temporarily idled	$ 23.9
Workers' Compensation Discount, Percent	1.00%	1.75%
Workers compensation liability	$ 30.3	$ 29.2

Leases - Additional Information

Leases - Additional Information (Details)	6 Months Ended
	Jun. 30, 2020
Optional extension lease terms	20 years
Lease termination period	1 year
Lessee, operating leases, existence of option to extend	true
Lessee, operating leases, existence of option to terminate	true
Minimum
Remaining lease terms	1 year
Maximum
Remaining lease terms	13 years

Leases - Schedule of Lease Term

Leases - Schedule of Lease Terms and Discount Rates (Details)	Jun. 30, 2020
Leases [Abstract]
Finance Lease, Weighted Average Remaining Lease Term	5 years 6 months
Operating Lease, Weighted Average Remaining Lease Term	9 years 6 months
Finance Lease, Weighted Average Discount Rate, Percent	4.60%
Operating Lease, Weighted Average Discount Rate, Percent	5.40%

Leases - Schedule of Lease Asse

Leases - Schedule of Lease Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease assets	$ 28	$ 25.8
Finance lease assets	$ 6.1	$ 6.6
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentNet	us-gaap:PropertyPlantAndEquipmentNet
Total lease assets	$ 34.1	$ 32.4
Operating lease liabilities, current	$ 4.5	$ 3.9
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherAccruedLiabilitiesCurrent	us-gaap:OtherAccruedLiabilitiesCurrent
Finance lease liabilities, current	$ 1.3	$ 1.2
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherAccruedLiabilitiesCurrent	us-gaap:OtherAccruedLiabilitiesCurrent
Operating lease liabilities, noncurrent	$ 27	$ 25.2
Finance lease liabilities, noncurrent	$ 4.8	$ 5.4
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Total lease liabilities	$ 37.6	$ 35.7

Leases - Components of Lease Co

Leases - Components of Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Leases [Abstract]
Operating lease cost	$ 1.8	$ 1.8	$ 3.6	$ 3.8
Short-term lease cost	0.3	0.2	0.6	0.5
Amortization of leased assets	0.3	0.3	0.7	0.7
Interest on lease liabilities	0.1	0.1	0.2	0.2
Total lease cost	$ 2.5	$ 2.4	$ 5.1	$ 5.2

Leases - Schedule of Maturity o

Leases - Schedule of Maturity of Our Lease Liabilities (Details) $ in Millions	Jun. 30, 2020USD ($)
Operating Leases
Remainder of 2020	$ 3.1
2021	5.6
2022	4.8
2023	4.4
2024	4.1
2025	2.3
2026 and thereafter	16.9
Total minimum lease payments	41.2
Less: interest	(9.7)
Present value	31.5
Finance Leases
Remainder of 2020	0.8
2021	1.5
2022	1.2
2023	1.1
2024	0.7
2025	0.7
2026 and thereafter	0.9
Total minimum lease payments	6.9
Less: interest	(0.8)
Present value	$ 6.1

Employee Benefits - Additional

Employee Benefits - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Defined Benefit Plan Disclosure
Payment for Other Postretirement Benefits		$ 2,900,000	$ 2,100,000
Postretirement Health Coverage | Salaried VEBA
Defined Benefit Plan Disclosure
Maximum contribution threshold		2,900,000
Payment for Other Postretirement Benefits	$ 2,900,000
Level 2 | Fair Value, Measurements, Recurring
Defined Benefit Plan Disclosure
Fair value of deferred compensation assets		8,800,000		$ 8,100,000
Accrued salaries, wages and related expenses
Defined Benefit Plan Disclosure
Accrued salaries, wages and related expenses		$ 3,500,000

Employee Benefits - Summary of

Employee Benefits - Summary of Total Expense Related to All Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure
Defined contribution plan, cost	$ 1.7	$ 1.7	$ 5.6	$ 5.6
Deferred compensation arrangement with individual, compensation expense	0.8	0.3	0.4	1
Multiemployer plan, contributions by employer	1.2	1.2	2.5	2.4
Total other employee benefit plans	4.9	4.8	10.9	12.3
Postretirement Health Coverage | Salaried VEBA
Defined Benefit Plan Disclosure
Total net periodic postretirement benefit cost relating to Salaried VEBA	$ 1.2	$ 1.6	$ 2.4	$ 3.3

Employee Benefits - Summary o_2

Employee Benefits - Summary of Components of Net Periodic Postretirement Benefit Cost Relating to Salaried VEBA (Details) - Postretirement Health Coverage - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Salaried VEBA:
Interest cost	$ 0.7	$ 0.8	$ 1.3	$ 1.6
Expected return on plan assets	(0.7)	(0.7)	(1.4)	(1.3)
Amortization of prior service cost	1.1	1.4	2.3	2.8
Amortization of net actuarial loss	0.1	0.1	0.2	0.2
Salaried VEBA
Salaried VEBA:
Total net periodic postretirement benefit cost relating to Salaried VEBA	$ 1.2	$ 1.6	$ 2.4	$ 3.3

Derivatives, Hedging Programs_3

Derivatives, Hedging Programs and Other Financial Instruments - Additional Information (Details) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Collateral posted for net derivatives	$ 0	$ 0
Cash collateral posted from customers	500,000	200,000
Designated as Hedging Instrument | Purchase
Derivative [Line Items]
Derivative net liability	$ 14,400,000	$ 7,200,000

Derivatives, Hedging Programs_4

Derivatives, Hedging Programs and Other Financial Instruments - Summary of Derivative Positions (Details) - Designated as Hedging Instrument mmlb in Millions	6 Months Ended
	Jun. 30, 2020mmlbMMBTUMWheuro
Purchase | Aluminum
Derivative [Line Items]
Derivative non-monetary notional amount	92.4
Purchase | Aluminum | Minimum
Derivative [Line Items]
Derivative maturity period	2020-07
Purchase | Aluminum | Maximum
Derivative [Line Items]
Derivative maturity period	2022-12
Purchase | Midwest premium swap contracts
Derivative [Line Items]
Derivative non-monetary notional amount	91.5
Purchase | Midwest premium swap contracts | Minimum
Derivative [Line Items]
Derivative maturity period	2020-07
Purchase | Midwest premium swap contracts | Maximum
Derivative [Line Items]
Derivative maturity period	2022-12
Purchase | Alloying Metals
Derivative [Line Items]
Derivative non-monetary notional amount	14.5
Purchase | Alloying Metals | Minimum
Derivative [Line Items]
Derivative maturity period	2020-07
Purchase | Alloying Metals | Maximum
Derivative [Line Items]
Derivative maturity period	2021-12
Purchase | Natural Gas
Derivative [Line Items]
Derivative non-monetary notional amount | MMBTU	7,490,000
Purchase | Natural Gas | Minimum
Derivative [Line Items]
Derivative maturity period	2020-07
Purchase | Natural Gas | Maximum
Derivative [Line Items]
Derivative maturity period	2024-12
Purchase | Foreign Exchange Contract
Derivative [Line Items]
Derivative non-monetary notional amount | euro	711,324
Purchase | Foreign Exchange Contract | Minimum
Derivative [Line Items]
Derivative maturity period	2020-09
Purchase | Foreign Exchange Contract | Maximum
Derivative [Line Items]
Derivative maturity period	2021-01
Purchase | Electricity
Derivative [Line Items]
Derivative non-monetary notional amount | MWh	570,140
Purchase | Electricity | Minimum
Derivative [Line Items]
Derivative maturity period	2020-07
Purchase | Electricity | Maximum
Derivative [Line Items]
Derivative maturity period	2022-12
Sales | Aluminum
Derivative [Line Items]
Derivative non-monetary notional amount	0.9
Sales | Aluminum | Minimum
Derivative [Line Items]
Derivative maturity period	2020-07
Sales | Aluminum | Maximum
Derivative [Line Items]
Derivative maturity period	2021-11
Sales | Alloying Metals
Derivative [Line Items]
Derivative non-monetary notional amount	5.8
Sales | Alloying Metals | Minimum
Derivative [Line Items]
Derivative maturity period	2020-07
Sales | Alloying Metals | Maximum
Derivative [Line Items]
Derivative maturity period	2021-12

Derivatives, Hedging Programs_5

Derivatives, Hedging Programs and Other Financial Instruments - Summary of Derivative Positions (Parenthetical) (Details) - Scenario, Forecast	Dec. 31, 2026	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Electricity
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage					49.00%	58.00%	59.00%
Natural Gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage	25.00%	25.00%	85.00%	93.00%	95.00%	91.00%	83.00%

Derivatives, Hedging Programs_6

Derivatives, Hedging Programs and Other Financial Instruments - Summary of Loss (Gain) Associated with Derivative Contracts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments Gain Loss [Line Items]
Total of income and expense line items presented in our Statements of Consolidated (Loss) Income in which the effects of cash flow hedges are recorded	$ 224.5	$ 303.5	$ 511.1	$ 618.6
Total of income and expense line items presented in our Statements of Consolidated (Loss) Income in which the effects of fair value hedges are recorded	13	12.1	26.2	24
Depreciation and Amortization | Designated as Hedging Instrument | Foreign Exchange Contract
Derivative Instruments Gain Loss [Line Items]
Foreign exchange contracts	(0.2)
Cash Flow Hedges | Cost of Sales | Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
Loss recognized in our Statements of Consolidated (Loss) Income related to cash flow hedges	10.5	4.7	17.5	8.9
Cash Flow Hedges | Cost of Sales | Designated as Hedging Instrument | Electricity
Derivative Instruments Gain Loss [Line Items]
Loss recognized in our Statements of Consolidated (Loss) Income related to cash flow hedges	0.3		0.5
Cash Flow Hedges | Cost of Sales | Designated as Hedging Instrument | Aluminum
Derivative Instruments Gain Loss [Line Items]
Loss recognized in our Statements of Consolidated (Loss) Income related to cash flow hedges	7.6	4.5	13.3	8.7
Cash Flow Hedges | Cost of Sales | Designated as Hedging Instrument | Alloying Metals
Derivative Instruments Gain Loss [Line Items]
Loss recognized in our Statements of Consolidated (Loss) Income related to cash flow hedges	1.5	0.1	2.1	$ 0.2
Cash Flow Hedges | Cost of Sales | Designated as Hedging Instrument | Alloying Metals (Reclassification Due To Forecasted Transactions No Longer Probable of Occuring
Derivative Instruments Gain Loss [Line Items]
Alloying metals (reclassification due to forecasted transactions no longer probable of occurring)	0.7		0.7
Cash Flow Hedges | Cost of Sales | Designated as Hedging Instrument | Natural Gas
Derivative Instruments Gain Loss [Line Items]
Loss recognized in our Statements of Consolidated (Loss) Income related to cash flow hedges	0.4	$ 0.1	0.9
Fair Value Hedges | Depreciation and Amortization | Designated as Hedging Instrument | Foreign Exchange Contract
Derivative Instruments Gain Loss [Line Items]
Loss recognized in our Statements of Consolidated (Loss) Income related to cash flow hedges	0.1		0.3
Hedged item	0.2
Excluded component amortized from AOCI	0.2		0.4
Reclassification from AOCI related to early termination of firm commitment	(0.4)		(0.4)
Net settlement related to early termination of forward contracts	$ 0.3		$ 0.3

Derivatives, Hedging Programs_7

Derivatives, Hedging Programs and Other Financial Instruments - Schedule of Fair Value of Derivative Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Designated as Hedging Instrument | Purchase
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative liability	$ (14.4)	$ (7.2)
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	2	4
Derivative liability	(16.4)	(11.2)
Fair Value, Measurements, Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	2	4
Derivative liability	(16.4)	(11.2)
Net Amount	(14.4)	(7.2)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 2 | Designated as Hedging Instrument | Purchase | Aluminum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	0.3	1
Derivative liability	(6.7)	(4.1)
Net Amount	(6.4)	(3.1)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 2 | Designated as Hedging Instrument | Purchase | Midwest premium swap contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	0.1	0
Derivative liability	(2.7)	(1.2)
Net Amount	(2.6)	(1.2)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 2 | Designated as Hedging Instrument | Purchase | Alloying Metals
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	0.2	0.4
Derivative liability	(1.7)	(1.5)
Net Amount	(1.5)	(1.1)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 2 | Designated as Hedging Instrument | Purchase | Natural Gas
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	0.2	0
Derivative liability	(2.7)	(2.8)
Net Amount	(2.5)	(2.8)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 2 | Designated as Hedging Instrument | Purchase | Electricity
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	1.1	2.6
Derivative liability	(2.6)	(1.6)
Net Amount	(1.5)	1
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 2 | Designated as Hedging Instrument | Sales | Aluminum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative asset	0.1	0
Derivative liability	0	0
Net Amount	$ 0.1	$ 0

Derivatives, Hedging Programs_8

Derivatives, Hedging Programs and Other Financial Instruments - Schedule of Total Amounts of Derivative Assets and Liabilities on Balance Sheets (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Derivative asset	$ 2	$ 4
Derivative liability	(16.4)	(11.2)
Prepaid Expenses and Other Current Assets
Derivative [Line Items]
Derivative asset	1.2	2.1
Other Assets
Derivative [Line Items]
Derivative asset	0.8	1.9
Other Accrued Liabilities
Derivative [Line Items]
Derivative liability	(9.8)	(7.6)
Long-term Liabilities
Derivative [Line Items]
Derivative liability	$ (6.6)	$ (3.6)

Derivatives, Hedging Programs_9

Derivatives, Hedging Programs and Other Financial Instruments - Schedule of Other Financial Assets Classifies under Appropriate Level of Fair Value Hierarchy (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 710.6	$ 264.3
Total	710.6	343
Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		78.7
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	710.6	28.2
Total	710.6	28.2
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	236.1
Total	0	314.8
Level 2 | Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		$ 78.7
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	0
Total	$ 0

Debt and Credit Facility - Addi

Debt and Credit Facility - Additional Information (Details) - USD ($)	Dec. 18, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	May 01, 2020	Apr. 28, 2020	Dec. 31, 2019	Nov. 26, 2019	May 15, 2016
Debt Instrument
Interest expense capitalized		$ 200,000	$ 400,000	$ 500,000	$ 900,000
Revolving Credit Facility
Debt Instrument
Line of credit facility, maximum borrowing capacity		375,000,000		375,000,000
Senior Notes Due 2025 | Senior Notes
Debt Instrument
Debt instrument contractual rate (percent)						6.50%	6.50%
Debt issuance, percentage of principal amount						101.00%	100.00%
Debt principal amount		350,000,000		350,000,000		$ 50,000,000	$ 300,000,000
Unamortized debt issuance costs		5,900,000		5,900,000
Interest expense		$ 4,200,000		$ 4,200,000
Effective interest rate (percent)		6.80%		6.80%
Debt instrument, payment terms				Interest accrues on the 6.50% Senior Notes beginning April 28, 2020 at a rate of 6.50% per annum and is payable semiannually on May 1 and November 1 of each year. The first interest payment date is November 1, 2020
Debt instrument, frequency of interest payment				semiannually
Debt Instrument, first interest payment date				Nov. 1, 2020
Fair value of outstanding debt		$ 365,500,000		$ 365,500,000
Senior Notes Due 2025 | Senior Notes | On or After May 1, 2022
Debt Instrument
Redemption price as percentage of principal (percent)				103.25%
Senior Notes Due 2025 | Senior Notes | On or After May 1, 2023
Debt Instrument
Redemption price as percentage of principal (percent)				101.625%
Senior Notes Due 2025 | Senior Notes | On or After May 1, 2024
Debt Instrument
Redemption price as percentage of principal (percent)				100.00%
Senior Notes Due 2025 | Senior Notes | Prior to May 1, 2022
Debt Instrument
Redemption price as percentage of principal (percent)				106.50%
Percentage of principal that can be redeemed (percent)				40.00%
Senior Notes Due 2028 | Senior Notes
Debt Instrument
Debt instrument contractual rate (percent)									4.625%
Debt issuance, percentage of principal amount									100.00%
Debt principal amount									$ 500,000,000
Unamortized debt issuance costs		7,000,000		$ 7,000,000
Interest expense		$ 6,000,000		$ 12,000,000
Effective interest rate (percent)		4.80%		4.80%
Fair value of outstanding debt		$ 482,200,000		$ 482,200,000				$ 513,500,000
Senior Notes Due 2024 | Senior Notes
Debt Instrument
Debt instrument contractual rate (percent)										5.875%
Debt issuance, percentage of principal amount										100.00%
Debt principal amount										$ 375,000,000
Interest expense			$ 5,700,000		$ 11,400,000
Effective interest rate (percent)			6.10%		6.10%
Senior Notes Due 2024 | Senior Notes | On or After May 15, 2019
Debt Instrument
Redemption price as percentage of principal (percent)	104.406%

Debt and Credit Facility - Sche

Debt and Credit Facility - Schedule of Availability and Usage of Revolving Credit Facility (Details) - Revolving Credit Facility	Jun. 30, 2020USD ($)
Line Of Credit Facility [Line Items]
Revolving Credit Facility borrowing commitment	$ 375,000,000
Borrowing base availability	290,000,000
Less: Outstanding borrowings under Revolving Credit Facility	0
Less: Outstanding letters of credit under Revolving Credit Facility	(7,700,000)
Remaining borrowing availability	$ 282,300,000
Borrowing rate (if applicable)	3.50%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Environmental Contingency
Short-term environmental accrual	$ 6.6	$ 5.5
Environmental accrual	$ 18.2
Expected period related to remediation expenditures for environmental contingencies period	30 years
Potential increase in environmental costs	$ 11.6
Time period within which recorded estimate of its obligation may change	12 months
Comprehensive Environmental Response, Compensation and Liability Act
Environmental Contingency
Short-term environmental accrual	$ 1.9
Minimum
Environmental Contingency
Period for final feasibility study	12 months
Maximum
Environmental Contingency
Period for final feasibility study	24 months

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 721.1	$ 733.9	$ 747.9	$ 740.4	$ 733.9	$ 740.4
Other comprehensive income (loss), net of tax	11.9	(15.5)	(3.2)	9.7	(3.6)	6.5
Ending balance	718.8	721.1	746.3	747.9	718.8	746.3
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(32.1)	(33.2)	(34.5)	(35.6)	(33.2)	(35.6)
Less: income tax (expense) benefit	(0.3)		(0.4)		(0.6)	(0.8)
Net loss (gain) reclassified from AOCI to Net (loss) income	0.9		1.1		1.9	2.2
Translation impact on Canadian pension plan AOCI balance					0.1
Other comprehensive income (loss), net of tax	0.9		1.1		2	2.2
Ending balance	(31.2)	(32.1)	(33.4)	(34.5)	(31.2)	(33.4)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI	0.1		0.1		0.2	0.2
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI	1.1		1.4		2.3	2.8
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.1	0.3	0.1	0.3	0.3	0.3
Unrealized gain (loss) on securities	0.1		0.7		1.4	1.7
Less: income tax benefit (expense)			(0.1)		(0.3)	(0.4)
Net unrealized (loss) gain on cash flow hedges	0.1		0.6		1.1	1.3
Reclassification from AOCI	(0.6)		(0.9)		(2.1)	(2.1)
Less: income tax (expense) benefit	0.2		0.2		0.5	0.5
Net loss (gain) reclassified from AOCI to Net (loss) income	(0.4)		(0.7)		(1.6)	(1.6)
Other comprehensive income (loss), net of tax	(0.3)		(0.1)		(0.5)	(0.3)
Ending balance	(0.2)	0.1		0.1	(0.2)
AOCI, Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(21.5)	(5.6)	(4.6)	(13.4)	(5.6)	(13.4)
Unrealized gain (loss) on securities	4.1		(10.1)		(23.8)	(2.7)
Less: income tax benefit (expense)	(0.9)		2.4		5.9	0.6
Net unrealized (loss) gain on cash flow hedges	3.2		(7.7)		(17.9)	(2.1)
Reclassification from AOCI	9.3		4.7		16.3	8.9
Reclassification due to forecasted sales no longer probable	0.7				0.7
Less: income tax (expense) benefit	(2.4)		(1.2)		(4.2)	(2.2)
Net loss (gain) reclassified from AOCI to Net (loss) income	7.6		3.5		12.8	6.7
Other comprehensive income (loss), net of tax	10.8		(4.2)		(5.1)	4.6
Ending balance	(10.7)	(21.5)	(8.8)	(4.6)	(10.7)	(8.8)
AOCI, Excluded Component of Derivative Qualifying as Fair Value Hedge Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(0.5)
Unrealized gain (loss) on securities	(0.2)				(1)
Less: income tax benefit (expense)					0.2
Net unrealized (loss) gain on cash flow hedges	(0.2)				(0.8)
Reclassification from AOCI	0.2				0.4
Reclassification due to cancellation of firm commitment	0.6				0.6
Less: income tax (expense) benefit	(0.1)				(0.2)
Net loss (gain) reclassified from AOCI to Net (loss) income	0.7				0.8
Other comprehensive income (loss), net of tax	0.5
Ending balance		(0.5)
AOCI, Accumulated Foreign Currency Adjustment Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(0.1)	(0.1)	(0.1)	(0.1)	(0.1)	(0.1)
Ending balance	(0.1)	(0.1)	(0.1)	(0.1)	(0.1)	(0.1)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(54.1)	(38.6)	(39.1)	(48.8)	(38.6)	(48.8)
Other comprehensive income (loss), net of tax	11.9	(15.5)	(3.2)	9.7
Ending balance	$ (42.2)	$ (54.1)	$ (42.3)	$ (39.1)	$ (42.2)	$ (42.3)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)
Equity [Abstract]
Estimated net mark-to-market loss before tax within next twelve months - cash flow hedges	$ 8.8

Restructuring - Summary of Acti

Restructuring - Summary of Activity Relating to Restructuring Plan Liabilities (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Restructuring And Related Activities [Abstract]
Restructuring costs	$ 11.9	$ 11.9
Cash payments		(1.4)
Ending balance	$ 10.5	$ 10.5

Other Income (Expense), Net (De

Other Income (Expense), Net (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Other Income And Expenses [Abstract]
Interest income	$ 0.2	$ 0.1	$ 0.3	$ 0.3
Net periodic postretirement benefit cost relating to Salaried VEBA	(1.2)	(1.6)	(2.4)	(3.3)
Realized gain on available for sale securities	0.6	1.2	2.1	2.4
Unrealized gain on equity securities	0.7		0.1	0.5
All other income (expense), net	0.2	0.2	(0.4)	0.5
Other income (expense), net	$ 0.5	$ (0.1)	$ (0.3)	$ 0.4

Income Tax Matters - Schedule o

Income Tax Matters - Schedule of Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Domestic	$ 1	$ 6.8	$ 10.6	$ 16.3
Foreign	0.3	0.5	0.3	0.8
Total	$ 1.3	$ 7.3	$ 10.9	$ 17.1

Income Tax Matters - Additional

Income Tax Matters - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax provision	$ 1.3	$ 7.3	$ 10.9	$ 17.1
Effective tax rate (percent)	(24.00%)	27.00%	33.00%	27.00%
Effective tax rate reconciliation, increase (decrease) to the valuation allowance for certain state net operating losses	$ 1		$ 1.3	$ 0.8
Effective tax rate reconciliation, increase (decrease) to the valuation allowance for certain state net operating losses (percent)	19.00%		4.00%	1.00%
Effective tax rate reconciliation, change in forecasted earnings	$ 1.9
Effective income tax rate reconciliation, change in forecasted earnings percent	37.00%
Effective income tax rate reconciliation, nondeductible expense, amount		$ 0.5	$ 0.8	$ 0.9
Effective income tax rate reconciliation, nondeductible expense, percent		2.00%	2.00%	2.00%
Effective tax rate reconciliation, unrecognized tax benefit amount		$ 0.2
Effective income tax rate reconciliation, unrecognized tax benefit percent		1.00%
Effective income tax rate reconciliation, tax expense (benefit), share-based payment arrangement, amount			$ (0.6)	$ (0.5)
Effective income tax rate reconciliation, tax expense (benefit), share-based payment arrangement, percent			2.00%	1.00%
Gross unrecognized tax benefits	$ 3.9		$ 3.9		$ 4.1
Gross unrecognized tax benefits that would impact effective tax rate	$ 0.4		$ 0.4		$ 0.9

Net (Loss) Income Per Share - S

Net (Loss) Income Per Share - Schedule of Calculation of Basic and Diluted Net (Loss) Income Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net (loss) income	$ (6.6)	$ 29.1	$ 19.2	$ 28	$ 22.5	$ 47.2
Denominator – Weighted-average common shares outstanding (in thousands):
Basic	15,781,000		16,063,000		15,809,000	16,085,000
Add: dilutive effect of non-vested common shares, restricted stock units and performance shares			177,000		120,000	213,000
Diluted	15,781,000		16,240,000		15,929,000	16,298,000
Net (loss) income per common share, Basic:	$ (0.41)		$ 1.19		$ 1.42	$ 2.93
Net (loss) income per common share, Diluted:	$ (0.41)		$ 1.18		$ 1.41	$ 2.89

Net (Loss) Income Per Share -_2

Net (Loss) Income Per Share - Schedule of Calculation of Basic and Diluted Net (Loss) Income Per Share (Parenthetical) (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share, amount	71,000	9,000	38,000	5,000

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Schedule of Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Interest paid	$ 6.1	$ 10.7
Non-cash investing and financing activities (included in Accounts payable):
Unpaid purchases of property and equipment	2.2	2.4
Stock repurchases not yet settled		0.3
Supplemental lease disclosures:
Operating lease liabilities arising from obtaining operating lease assets	4.6	0.9
Cash paid for amounts included in the measurement of operating lease liabilities	2.3	1.8
Finance lease liabilities arising from obtaining finance lease assets	0.3	0.5
Components of cash, cash equivalents and restricted cash:
Cash and cash equivalents	710.6	122.4	$ 264.3
Restricted cash included in Prepaid expenses and other current assets		0.3
Restricted cash included in Other assets	14	14.2
Total cash, cash equivalents and restricted cash presented on our Statements of Consolidated Cash Flows	$ 724.6	$ 136.9	$ 278.6	$ 139.6

Business, Product and Geograp_3

Business, Product and Geographical Area Information - Additional Information (Details)	6 Months Ended
	Jun. 30, 2020Productionfacility
Domestic
Segment Reporting Information [Line Items]
Number of production facilities	12
Foreign
Segment Reporting Information [Line Items]
Number of production facilities	1

Business, Product and Geograp_4

Business, Product and Geographical Area Information - Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net sales:
Net sales	$ 275.7	$ 375.3	$ 645	$ 770.5
Transferred at Point in Time
Net sales:
Net sales	164.7	222.6	380.3	445.9
Transferred over Time
Net sales:
Net sales	111	152.7	264.7	324.6
Aero/HS products
Net sales:
Net sales	144.6	189.4	340.6	387.9
Automotive Extrusions
Net sales:
Net sales	16.7	45.5	64.1	98.5
GE products
Net sales:
Net sales	110.8	128.2	232.5	258.2
Other products
Net sales:
Net sales	$ 3.6	$ 12.2	$ 7.8	$ 25.9

Business, Product and Geograp_5

Business, Product and Geographical Area Information - Net Sales by End Market Segment Applications (Details) (Parenthetical) (Details) - Previously Reported - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Transferred at Point in Time
Net sales:
Revenue from Contract with Customer, Excluding Assessed Tax	$ 131	$ 262.8
Transferred over Time
Net sales:
Revenue from Contract with Customer, Excluding Assessed Tax	$ 244.3	$ 507.7

Business, Product and Geograp_6

Business, Product and Geographical Area Information - Schedule of Income Taxes Paid by Geographical Area (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Income taxes paid	$ 0.3	$ 2.2	$ 0.4	$ 3.1
Domestic
Segment Reporting Information [Line Items]
Income taxes paid	0.3	1.8	0.3	1.9
Foreign
Segment Reporting Information [Line Items]
Income taxes paid	$ 0	$ 0.4	$ 0.1	$ 1.2

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 14, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019
Subsequent Event [Line Items]
Cash dividends declared (in dollars per share)		$ 0.67	$ 0.67	$ 0.60	$ 0.60
Subsequent Event
Subsequent Event [Line Items]
Cash dividends declared (in dollars per share)	$ 0.67
Cash dividends declared	$ 10.7
Cash dividends, declared date	Jul. 14, 2020
Cash dividends, payable date	Aug. 14, 2020
Cash dividends, record date	Jul. 24, 2020