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	42.9		42.9
Repurchase of common stock	(10.0)			(10.0)
Payments to taxing authorities in consideration of employee tax obligations related to stock-based compensation arrangements	(2.2)	(2.2)
Stock-based compensation	2.4	2.4
Exercise of stock options	5.6	(8.8)		14.4
Other comprehensive (loss) income	(1.0)				(1.0)
Dividends declared	14.4		14.4
Ending balance at Mar. 31, 2017	395.7	479.4	647.8	(800.5)	65.4	3.6
Increase (Decrease) in Stockholders' Equity
Cumulative Effect of New Accounting Principle in Period of Adoption	3.2
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	43.4		43.6			(0.2)
Repurchase of common stock	(35.0)			(35.0)
Payments to taxing authorities in consideration of employee tax obligations related to stock-based compensation arrangements	(0.7)	(0.7)
Stock-based compensation	3.7	3.7
Exercise of stock options	0.8	(0.4)		1.2
Shares issued	0.0	(1.3)		1.3
Other comprehensive (loss) income	(16.6)				(16.6)
Dividends declared	16.2		16.2
Ending balance at Mar. 31, 2018	$ 245.9	$ 476.8	$ 603.7	$ (864.6)	$ 23.3	$ 6.7