CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDER'S EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Paid-in Capital	Retained Earnings	Other
Common Stock, Shares		52.9
Total stockholders’ equity at Dec. 31, 2019	$ 1,376.2	$ 0.5	$ 638.0	$ 744.7	$ (7.0)
Vesting of restricted stock units, shares		0.1
Vesting of restricted stock units, value	(4.9)		(4.9)
Employee stock purchase plan, shares		0.2
Employee stock purchase plan, value	5.9		5.9
Stock-based compensation expense	8.9		8.9
Stock Repurchased and Retired During Period, Shares		(0.8)
Stock Repurchased and Retired During Period, Value	(27.9)		(9.2)	(18.7)
Foreign currency translation adjustments	(2.5)				(2.5)
Net income	43.8			43.8
Shares Outstanding at Mar. 31, 2020		52.4
Total stockholders’ equity at Mar. 31, 2020	1,399.5	$ 0.5	638.7	769.8	(9.5)
Common Stock, Shares		52.9
Total stockholders’ equity at Dec. 31, 2020	1,587.1	$ 0.5	661.3	926.3	(1.0)
Vesting of restricted stock units, shares		0.1
Vesting of restricted stock units, value	(4.8)		(4.8)
Employee stock purchase plan, shares		0.2
Employee stock purchase plan, value	7.6		7.6
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	0.1		0.1
Stock-based compensation expense	10.3		10.3
Foreign currency translation adjustments	(3.2)				(3.2)
Net income	48.7			48.7
Shares Outstanding at Mar. 31, 2021		53.2
Total stockholders’ equity at Mar. 31, 2021	$ 1,645.8	$ 0.5	$ 674.5	$ 975.0	$ (4.2)