Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock Par	Common Stock Additional Paid-In Capital	Common Stock Accumulated Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Balance at Dec. 31, 2014	$ 1,149.9	$ 1.0	$ 678.5	$ 845.5	$ (69.7)	$ (305.4)
Increase (Decrease) in Stockholders' Equity
Net income	237.2			237.2
Dividends paid on common stock	(38.3)			(38.3)
Change in other comprehensive income – net of tax	(54.2)				(54.2)
Stock based compensation	37.4	0.1	37.3
Acquisition of treasury stock	(152.4)					(152.4)
Balance at Dec. 31, 2015	1,179.6	1.1	715.8	1,044.4	(123.9)	(457.8)
Increase (Decrease) in Stockholders' Equity
Net income	249.8			249.8
Dividends paid on common stock	(39.8)			(39.8)
Change in other comprehensive income – net of tax	(50.5)				(50.5)
Stock based compensation	23.0		23.0
Adoption of ASU 2016-09	0.3			0.3
Acquisition of treasury stock	(117.5)					(117.5)
Balance at Dec. 31, 2016	1,244.9	1.1	738.8	1,254.7	(174.4)	(575.3)
Increase (Decrease) in Stockholders' Equity
Net income	284.0			284.0
Dividends paid on common stock	(42.6)			(42.6)
Change in other comprehensive income – net of tax	129.4				129.4
Stock based compensation	35.5		35.5
Acquisition of treasury stock	(156.1)					(156.1)
Balance at Dec. 31, 2017	$ 1,495.1	$ 1.1	$ 774.3	$ 1,496.1	$ (45.0)	$ (731.4)