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	86.4		86.8			(0.4)
Repurchase of common stock	(30.0)			(30.0)
Payments to taxing authorities in consideration of employee tax obligations related to stock-based compensation arrangements	(2.4)	(2.4)
Stock-based compensation	5.4	5.4
Exercise of stock options	11.8	(17.0)		28.8
Shares issued	0.7	0.7
Other comprehensive (loss) income	(9.9)				(9.9)
Dividends declared	(28.8)		(28.8)
Ending balance at Jun. 30, 2017	405.6	474.7	677.3	(806.1)	56.5	3.2
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	82.0		82.4			(0.4)
Repurchase of common stock	(49.8)			(49.8)
Payments to taxing authorities in consideration of employee tax obligations related to stock-based compensation arrangements	(3.0)	(3.0)
Stock-based compensation	9.6	9.6
Exercise of stock options	6.1	(4.1)		10.2
Shares issued	0.8	(5.2)		6.0
Other comprehensive (loss) income	15.9				15.9
Dividends declared	(32.5)		(32.5)
Ending balance at Jun. 30, 2018	$ 294.9	$ 472.8	$ 625.5	$ (865.7)	$ 55.8	$ 6.5