Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Other Capital	Treasury Stock	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2019		77.3
Beginning balance at Dec. 31, 2019	$ 576.7	$ 7.7	$ 573.3	$ (12.7)	$ 244.9	$ (236.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	102.3				102.3
Amortization of net actuarial losses and prior service costs, net of income taxes	30.3					30.3
Purchase of treasury stock (in shares)		(0.3)
Purchase of treasury stock	(12.3)			(12.3)
Repurchase of shares for withholding taxes and option costs under equity plans (in shares)		(0.2)
Repurchase of shares for withholding taxes and option costs under equity plans	(8.8)		(8.8)
Stock-based compensation and shares issued under equity plans (in shares)		0.6
Stock-based compensation and shares issued under equity plans	20.7		20.7
Ending balance (in shares) at Sep. 30, 2020		77.4
Ending balance at Sep. 30, 2020	708.9	$ 7.7	585.2	(25.0)	347.2	(206.2)
Beginning balance (in shares) at Jun. 30, 2020		77.6
Beginning balance at Jun. 30, 2020	671.3	$ 7.7	577.6	(13.2)	315.5	(216.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	31.7				31.7
Amortization of net actuarial losses and prior service costs, net of income taxes	10.1					10.1
Purchase of treasury stock (in shares)		(0.3)
Purchase of treasury stock	(11.8)			(11.8)
Repurchase of shares for withholding taxes and option costs under equity plans	(0.6)		(0.6)
Stock-based compensation and shares issued under equity plans (in shares)		0.1
Stock-based compensation and shares issued under equity plans	8.2		8.2
Ending balance (in shares) at Sep. 30, 2020		77.4
Ending balance at Sep. 30, 2020	708.9	$ 7.7	585.2	(25.0)	347.2	(206.2)
Beginning balance (in shares) at Dec. 31, 2020		76.8
Beginning balance at Dec. 31, 2020	233.5	$ 7.7	583.0	(64.4)	(65.2)	(227.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	105.7				105.7
Amortization of net actuarial losses and prior service costs, net of income taxes	34.5					34.5
Adjustment to dividends paid	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	400.3	$ 8.0	596.0	(64.4)	53.8	(193.1)
Beginning balance (in shares) at Jun. 30, 2021		79.8
Beginning balance at Jun. 30, 2021	339.1	$ 8.0	588.9	(64.4)	11.2	(204.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	42.6				42.6
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	$ 400.3	$ 8.0	$ 596.0	$ (64.4)	$ 53.8	$ (193.1)