Consolidated Statement of Equity - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Non Controlling Interests
Balance at Dec. 31, 2016	$ 696.8		$ (667.9)	$ 584.0	$ 861.9	$ (81.5)	$ 0.3
Balance (in shares) at Dec. 31, 2016		42,932,994
Increase (Decrease) in Stockholders' Equity
Consolidated net income	136.9				136.9		0.0
Other Comprehensive Income (loss)
Unrealized gain on available-for-sale investments, net of income tax	3.4					3.4
Reclassification of adjustments for gains included in net income, net of income tax	(1.9)					(1.9)
Foreign currency translation adjustment, net	33.4					33.4	0.0
Other comprehensive income (loss)	34.9					34.9	0.0
Issuance of common stock related to stock-option exercises and vesting of restricted stock units, net	(4.6)		1.6	(6.2)
Issuance of common stock related to stock-option exercises and vesting of restricted stock units, net (in shares)		161,445
APIC, Share-based Payment Arrangement, Increase for Cost Recognition [Abstract]
Stock-based compensation — restricted stock units	16.5			16.5
Stock-based compensation — performance share awards	7.1			7.1
Stock-based compensation — performance share awards	0.5			0.5
Dividends declared ($1.14 per share)	(40.1)				(40.1)
Purchase of additional interest in majority-owned investment	(1.2)			(0.9)			(0.3)
Common share repurchased	(41.9)		(41.9)
Common share repurchased (in shares)		(546,732)
Balance at Dec. 31, 2017	804.9		(708.2)	601.0	958.7	(46.6)	0.0
Balance (in shares) at Dec. 31, 2017		42,547,707
Cumulative Effect on Retained Earnings, Net of Tax	17.0				17.0
Increase (Decrease) in Stockholders' Equity
Consolidated net income	183.0				183.0		0.0
Other Comprehensive Income (loss)
Unrealized gain on available-for-sale investments, net of income tax	(1.0)					(1.0)
Reclassification of adjustments for gains included in net income, net of income tax	(0.8)					(0.8)
Foreign currency translation adjustment, net	(26.6)					(26.6)	0.0
Other comprehensive income (loss)	(28.4)					(28.4)	0.0
Issuance of common stock related to stock-option exercises and vesting of restricted stock units, net	(13.2)		2.3	(15.5)
Reclassification of awards previously liability-classified that were converted to equity	4.5			4.5
Issuance of common stock related to stock-option exercises and vesting of restricted stock units, net (in shares)		278,656
APIC, Share-based Payment Arrangement, Increase for Cost Recognition [Abstract]
Stock-based compensation — restricted stock units	19.8			19.8
Stock-based compensation — performance share awards	10.2			10.2
Stock-based compensation — market stock units	1.7			1.7
Dividends declared ($1.14 per share)	(43.9)				(43.9)
Common share repurchased	(20.9)		(20.9)
Common share repurchased (in shares)		(202,245)
Balance at Dec. 31, 2018	$ 934.7	$ 0.0	(726.8)	621.7	1,114.8	(75.0)	0.0
Balance (in shares) at Dec. 31, 2018	46,624,118	42,624,118
Increase (Decrease) in Stockholders' Equity
Consolidated net income	$ 152.0				152.0		0.0
Other Comprehensive Income (loss)
Unrealized gain on available-for-sale investments, net of income tax	3.8					3.8
Reclassification of adjustments for gains included in net income, net of income tax	(0.9)					(0.9)
Foreign currency translation adjustment, net	11.5					11.5	0.0
Other comprehensive income (loss)	14.4					14.4	0.0
Issuance of common stock related to stock-option exercises and vesting of restricted stock units, net	(15.2)		2.7	(17.9)
Reclassification of awards previously liability-classified that were converted to equity	6.8			6.8
Issuance of common stock related to stock-option exercises and vesting of restricted stock units, net (in shares)		266,176
APIC, Share-based Payment Arrangement, Increase for Cost Recognition [Abstract]
Stock-based compensation — restricted stock units	20.4			20.4
Stock-based compensation — performance share awards	20.6			20.6
Stock-based compensation — market stock units	3.4			3.4
Dividends declared ($1.14 per share)	(48.9)				(48.9)
Common share repurchased	(4.6)		(4.6)
Common share repurchased (in shares)		(41,935)
Balance at Dec. 31, 2019	$ 1,083.6	$ 0.0	$ (728.7)	$ 655.0	$ 1,217.9	$ (60.6)	$ 0.0
Balance (in shares) at Dec. 31, 2019	42,848,359	42,848,359