Condensed Consolidated Statement of Equity - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Balance at Dec. 31, 2018	$ 934.7	$ 0.0	$ (726.8)	$ 621.7	$ 1,114.8	$ (75.0)
Balance (in shares) at Dec. 31, 2018		42,624,118
Increase (Decrease) in Stockholders' Equity
Net income	33.2				33.2
Other comprehensive loss:
Unrealized loss on available-for-sale investments, net of income tax of $1.4	1.9					1.9
Reclassification of adjustments for gain included in net income, net of income tax	(0.5)					(0.5)
Foreign currency translation adjustment	3.4					3.4
Other comprehensive loss	4.8					4.8
Issuance of common stock related to stock-option exercises and vesting of restricted stock units, net of shares withheld for taxes on settlements of restricted stock units (in shares)		73,530
Vesting of restricted stock units, net of shares withheld for taxes on settlements of restricted stock units	(4.6)			(4.6)
Reclassification of awards previously liability-classified that were converted to equity	6.6			6.6
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition
Stock-based compensation	10.0			10.0
Common share repurchased (in shares)		(41,935)
Common shares repurchased	(4.6)		(4.6)
Dividends declared	(11.9)				(11.9)
Balance at Mar. 31, 2019	968.2	$ 0.0	(731.4)	633.7	1,136.1	(70.2)
Balance (in shares) at Mar. 31, 2019		42,655,713
Balance at Dec. 31, 2019	$ 1,083.6	$ 0.0	(728.7)	655.0	1,217.9	(60.6)
Balance (in shares) at Dec. 31, 2019	42,848,359	42,848,359
Increase (Decrease) in Stockholders' Equity
Net income	$ 23.9				23.9
Other comprehensive loss:
Unrealized loss on available-for-sale investments, net of income tax of $1.4	(4.1)					(4.1)
Reclassification of adjustments for gain included in net income, net of income tax	0.3					0.3
Foreign currency translation adjustment	(40.4)					(40.4)
Other comprehensive loss	(44.2)					(44.2)
Issuance of common stock related to stock-option exercises and vesting of restricted stock units, net of shares withheld for taxes on settlements of restricted stock units (in shares)		121,689
Vesting of restricted stock units, net of shares withheld for taxes on settlements of restricted stock units	(10.6)	$ 0.0	0.0	(10.6)
Reclassification of awards previously liability-classified that were converted to equity	5.5	$ 0.0	0.0	5.5	0.0	0.0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition
Stock-based compensation	7.3			7.3
Common share repurchased (in shares)		(176,925)
Common shares repurchased	(20.0)		(20.0)
Dividends declared	(12.8)				(12.8)
Balance at Mar. 31, 2020	$ 1,032.7	$ 0.0	$ (748.7)	$ 657.2	$ 1,229.0	$ (104.8)
Balance (in shares) at Mar. 31, 2020	42,793,123	42,793,123