Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Other Capital	Other Capital Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock	Retained Earnings (Accumulated Deficit)	Retained Earnings (Accumulated Deficit) Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2020			76.8
Beginning balance at Dec. 31, 2020	$ 220.4		$ 7.7	$ 562.1		$ (64.4)	$ (57.4)		$ (227.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	105.6						105.6
Amortization of net actuarial losses and prior service costs, net of income taxes	34.5								34.5
Adjustment to dividends	13.3						13.3
Settlement of debt (in shares)			2.9
Settlement of debt	(3.9)		$ 0.3	(4.2)
Repurchase of shares for withholding taxes and option costs under equity plans	(4.5)			(4.5)
Stock-based compensation and shares issued under equity plans (in shares)			0.4
Stock-based compensation and shares issued under equity plans	21.7			21.7
Ending balance (in shares) at Sep. 30, 2021			80.1
Ending balance at Sep. 30, 2021	387.1		$ 8.0	575.1		(64.4)	61.5		(193.1)
Beginning balance (in shares) at Dec. 31, 2020			76.8
Beginning balance at Dec. 31, 2020	$ 220.4		$ 7.7	562.1		(64.4)	(57.4)		(227.6)
Ending balance (in shares) at Dec. 31, 2021	80.1		80.1
Ending balance at Dec. 31, 2021	$ 523.3	$ (6.6)	$ 8.0	578.1	$ (5.6)	(64.4)	102.6	$ (1.0)	(101.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible Enumeration]	Accounting Standards Update 2020-06 [Member]
Beginning balance (in shares) at Jun. 30, 2021			79.8
Beginning balance at Jun. 30, 2021	$ 326.0		$ 8.0	568.0		(64.4)	19.0		(204.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	42.5						42.5
Amortization of net actuarial losses and prior service costs, net of income taxes	11.5								11.5
Settlement of debt (in shares)			0.2
Settlement of debt	(0.1)			(0.1)
Repurchase of shares for withholding taxes and option costs under equity plans	(0.5)			(0.5)
Stock-based compensation and shares issued under equity plans (in shares)			0.1
Stock-based compensation and shares issued under equity plans	7.7			7.7
Ending balance (in shares) at Sep. 30, 2021			80.1
Ending balance at Sep. 30, 2021	$ 387.1		$ 8.0	575.1		(64.4)	61.5		(193.1)
Beginning balance (in shares) at Dec. 31, 2021	80.1		80.1
Beginning balance at Dec. 31, 2021	$ 523.3	$ (6.6)	$ 8.0	578.1	$ (5.6)	(64.4)	102.6	$ (1.0)	(101.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	57.9						57.9
Amortization of net actuarial losses and prior service costs, net of income taxes	15.6								15.6
Adjustment to dividends	$ 0.9						0.9
Issuance of treasury stock (in shares)	0.1		0.1
Issuance of treasury stock	$ 3.3			1.9		1.4
Settlement of debt	(73.2)			(73.2)
Repurchase of shares for withholding taxes and option costs under equity plans (in shares)			(0.1)
Repurchase of shares for withholding taxes and option costs under equity plans	(4.7)			(4.7)
Stock-based compensation and shares issued under equity plans (in shares)			0.3
Stock-based compensation and shares issued under equity plans	$ 8.6			8.6
Ending balance (in shares) at Sep. 30, 2022	80.4		80.4
Ending balance at Sep. 30, 2022	$ 525.1		$ 8.0	505.1		(63.0)	160.4		(85.4)
Beginning balance (in shares) at Jun. 30, 2022			80.3
Beginning balance at Jun. 30, 2022	574.1		$ 8.0	574.5		(64.4)	146.6		(90.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	13.7						13.7
Amortization of net actuarial losses and prior service costs, net of income taxes	5.2								5.2
Adjustment to dividends	0.1						0.1
Issuance of treasury stock (in shares)			0.1
Issuance of treasury stock	3.3			1.9		1.4
Settlement of debt	(73.2)			(73.2)
Repurchase of shares for withholding taxes and option costs under equity plans	(0.4)			(0.4)
Stock-based compensation and shares issued under equity plans	$ 2.3			2.3
Ending balance (in shares) at Sep. 30, 2022	80.4		80.4
Ending balance at Sep. 30, 2022	$ 525.1		$ 8.0	$ 505.1		$ (63.0)	$ 160.4		$ (85.4)