Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Common Stock	Additional Paid In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Total
Balance at the beginning of the period at Dec. 31, 2015	$ 32.6	$ 287.9	$ (46.9)	$ 177.0	$ 450.6
Balance (in shares) at Dec. 31, 2015	43.5
Increase (Decrease) in Stockholders' Equity
Net income				81.4	81.4
Other comprehensive income (loss), net of tax			23.3		23.3
Tax benefit from stock-based compensation and share withholding		2.2			2.2
Share-based compensation		11.2			11.2
Shares issued	$ 0.2	(4.9)			(4.7)
Shares issued (in shares)	0.3
Shares repurchased	$ (0.7)	(6.6)		(29.6)	(36.9)
Shares repurchased (in shares)	(0.9)
Dividends ($0.82, $0.78, and $0.74 per share) for the years 2018, 2017 and 2016 respectively				(32.2)	(32.2)
Balance at the end of the period at Dec. 31, 2016	$ 32.1	289.8	(23.6)	196.6	494.9
Balance (in shares) at Dec. 31, 2016	42.9
Increase (Decrease) in Stockholders' Equity
Net income				231.0	231.0
Other comprehensive income (loss), net of tax			(1.3)		(1.3)
Share-based compensation		11.1			11.1
Shares issued	$ 0.3	(5.7)			(5.4)
Shares issued (in shares)	0.3
Shares repurchased	$ (0.5)	(5.5)		(13.3)	(19.3)
Shares repurchased (in shares)	(0.7)
Dividends ($0.82, $0.78, and $0.74 per share) for the years 2018, 2017 and 2016 respectively				(33.8)	(33.8)
Balance at the end of the period at Dec. 31, 2017	$ 31.9	289.7	(24.9)	380.5	$ 677.2
Balance (in shares) at Dec. 31, 2017	42.5				42.5
Increase (Decrease) in Stockholders' Equity
Net income				109.0	$ 109.0
Other comprehensive income (loss), net of tax			(9.6)	6.0	(3.6)
Share-based compensation		12.1			12.1
Shares issued	$ 0.1	(4.0)			(3.9)
Shares issued (in shares)	0.2
Shares repurchased				(0.1)	(0.1)
Dividends ($0.82, $0.78, and $0.74 per share) for the years 2018, 2017 and 2016 respectively				(35.4)	(35.4)
Balance at the end of the period at Dec. 31, 2018	$ 32.0	$ 297.8	$ (34.5)	$ 460.0	$ 755.3
Balance (in shares) at Dec. 31, 2018	42.7				42.7