Consolidated Statements of Equity (unaudited) - USD ($) $ in Millions	Total	Common Stock and Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests
Beginning balance at Dec. 31, 2016	$ 372.4	$ 488.0	$ 619.3	$ (804.9)	$ 66.4	$ 3.6
Increase (Decrease) in Stockholders' Equity
Net income	133.5		134.2			(0.7)
Repurchase of common stock	(65.0)			(65.0)
Payments to taxing authorities in consideration of employee tax obligations related to stock-based compensation arrangements	(2.5)	(2.5)
Stock-based compensation	8.2	8.2
Exercise of stock options	14.4	(18.3)		32.7
Shares issued	0.7	0.7
Other comprehensive (loss) income	(22.7)				(22.7)
Dividends declared	(43.2)		(43.2)
Noncontrolling Interest, Increase from Subsidiary Equity Issuance	1.2					1.2
Ending balance at Sep. 30, 2017	397.0	476.1	710.3	(837.2)	43.7	4.1
Increase (Decrease) in Stockholders' Equity
Adjustment to retained earnings for adoption of ASC 606	2.5		2.5
Beginning balance at Dec. 31, 2017	263.3	475.5	573.1	(832.1)	39.9	6.9
Increase (Decrease) in Stockholders' Equity
Net income	97.9		98.5			(0.6)
Repurchase of common stock	(60.1)			(60.1)
Payments to taxing authorities in consideration of employee tax obligations related to stock-based compensation arrangements	(2.9)	(2.9)
Stock-based compensation	14.5	14.5
Exercise of stock options	6.4	(4.2)		10.6
Shares issued	0.7	(5.2)		5.9
Other comprehensive (loss) income	6.6				6.6
Dividends declared	(48.7)		(48.7)
Ending balance at Sep. 30, 2018	$ 280.2	$ 477.7	$ 625.4	$ (875.7)	$ 46.5	$ 6.3