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, 2017	$ 263.3	$ 475.5	$ 573.1	$ (832.1)	$ 39.9	$ 6.9
Increase (Decrease) in Stockholders' Equity
Net income	43.4	0.0	43.6	0.0	0.0	(0.2)
Repurchase of common stock	(35.0)	0.0	0.0	(35.0)	0.0	0.0
Payments in consideration of employee tax obligations related to stock-based compensation	(0.7)	(0.7)	0.0	0.0	0.0	0.0
Stock-based compensation	3.7	3.7	0.0	0.0	0.0	0.0
Exercise of stock options	0.8	(0.4)	0.0	1.2	0.0	0.0
Shares issued	0.0	(1.3)	0.0	1.3	0.0	0.0
Dividends declared	(16.2)	0.0	(16.2)	0.0	0.0	0.0
Other comprehensive (loss) income	(16.6)	0.0	0.0	0.0	(16.6)	0.0
Ending balance at Mar. 31, 2018	245.9	476.8	603.7	(864.6)	23.3	6.7
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
Cash paid for repurchases of common stock	60.1
Other comprehensive (loss) income	6.6
Ending balance at Sep. 30, 2018	280.2	477.7	625.4	(875.7)	46.5	6.3
Increase (Decrease) in Stockholders' Equity
Adjustment to retained earnings for adoption of ASC 606 | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]	3.2	0.0	3.2	0.0	0.0	0.0
Beginning balance at Mar. 31, 2018	245.9	476.8	603.7	(864.6)	23.3	6.7
Increase (Decrease) in Stockholders' Equity
Net income	38.6	0.0	38.8	0.0	0.0	(0.2)
Repurchase of common stock	(14.8)	0.0	0.0	(14.8)	0.0	0.0
Payments in consideration of employee tax obligations related to stock-based compensation	(2.3)	(2.3)	0.0	0.0	0.0	0.0
Stock-based compensation	5.9	5.9	0.0	0.0	0.0	0.0
Exercise of stock options	5.3	(3.7)	0.0	9.0	0.0	0.0
Shares issued	0.8	(3.9)	0.0	4.7	0.0	0.0
Dividends declared	(16.3)	0.0	(16.3)	0.0	0.0	0.0
Other comprehensive (loss) income	32.5	0.0	0.0	0.0	32.5	0.0
Ending balance at Jun. 30, 2018	294.9	472.8	625.5	(865.7)	55.8	6.5
Increase (Decrease) in Stockholders' Equity
Adjustment to retained earnings for adoption of ASC 606 | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]	(0.7)	0.0	(0.7)	0.0	0.0	0.0
Net income	15.9	0.0	16.1	0.0	0.0	(0.2)
Repurchase of common stock	(10.3)	0.0	0.0	(10.3)	0.0	0.0
Payments in consideration of employee tax obligations related to stock-based compensation	0.1	0.1	0.0	0.0	0.0	0.0
Stock-based compensation	4.9	4.9	0.0	0.0	0.0	0.0
Exercise of stock options	0.3	(0.1)	0.0	0.4	0.0	0.0
Shares issued	(0.1)	0.0	0.0	(0.1)	0.0	0.0
Dividends declared	(16.2)	0.0	(16.2)	0.0	0.0	0.0
Other comprehensive (loss) income	(9.3)	0.0	0.0	0.0	(9.3)	0.0
Ending balance at Sep. 30, 2018	280.2	477.7	625.4	(875.7)	46.5	6.3
Beginning balance at Dec. 31, 2018	337.0	481.8	676.7	(895.5)	67.9	6.1
Increase (Decrease) in Stockholders' Equity
Net income	24.6	0.0	24.7	0.0	0.0	(0.1)
Repurchase of common stock	(4.8)	0.0	0.0	(4.8)	0.0	0.0
Payments in consideration of employee tax obligations related to stock-based compensation	(4.3)	(4.3)	0.0	0.0	0.0	0.0
Stock-based compensation	1.9	1.9	0.0	0.0	0.0	0.0
Exercise of stock options	9.2	(2.2)	0.0	11.4	0.0	0.0
Shares issued	(0.3)	(7.4)	0.0	7.1	0.0	0.0
Dividends declared	(18.1)	0.0	(18.1)	0.0	0.0	0.0
Other comprehensive (loss) income	8.6	0.0	0.0	0.0	8.6	0.0
Ending balance at Mar. 31, 2019	353.8	469.8	683.3	(881.8)	76.5	6.0
Beginning balance at Dec. 31, 2018	337.0	481.8	676.7	(895.5)	67.9	6.1
Increase (Decrease) in Stockholders' Equity
Net income	154.8
Cash paid for repurchases of common stock	29.8
Other comprehensive (loss) income	17.4
Ending balance at Sep. 30, 2019	451.7	475.4	776.9	(892.2)	85.3	6.3
Beginning balance at Mar. 31, 2019	353.8	469.8	683.3	(881.8)	76.5	6.0
Increase (Decrease) in Stockholders' Equity
Net income	76.4	0.0	76.2	0.0	0.0	0.2
Repurchase of common stock	(25.0)	0.0	0.0	(25.0)	0.0	0.0
Payments in consideration of employee tax obligations related to stock-based compensation	(0.6)	(0.6)	0.0	0.0	0.0	0.0
Stock-based compensation	3.7	3.7	0.0	0.0	0.0	0.0
Exercise of stock options	8.8	(2.4)	0.0	11.2	0.0	0.0
Shares issued	1.4	(0.5)	0.0	1.9	0.0	0.0
Dividends declared	(18.2)	0.0	(18.2)	0.0	0.0	0.0
Other comprehensive (loss) income	(13.0)	0.0	0.0	0.0	(13.0)	0.0
Ending balance at Jun. 30, 2019	387.3	470.0	741.3	(893.7)	63.5	6.2
Increase (Decrease) in Stockholders' Equity
Net income	53.8	0.0	53.7	0.0	0.0	0.1
Stock-based compensation	5.8	5.8	0.0	0.0	0.0	0.0
Exercise of stock options	1.1	(0.4)	0.0	1.5	0.0	0.0
Dividends declared	(18.1)	0.0	(18.1)	0.0	0.0	0.0
Other comprehensive (loss) income	21.8	0.0	0.0	0.0	21.8	0.0
Ending balance at Sep. 30, 2019	$ 451.7	$ 475.4	$ 776.9	$ (892.2)	$ 85.3	$ 6.3