CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDER'S EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Shares Outstanding at Dec. 31, 2018		52.5
Total stockholders’ equity at Dec. 31, 2018	$ 1,182.1	$ 0.5	$ 601.8	$ 586.1	$ (6.3)
Vesting of restricted stock units, shares		0.2
Vesting of restricted stock units, value	(6.8)		(6.8)
Employee stock purchase plan, shares		0.1
Employee stock purchase plan, value	6.9		6.9
Stock Issued During Period, Value, Stock Options Exercised	23.6
Stock-based compensation expense			23.6
Stock Repurchased and Retired During Period, Value	(0.1)
Foreign currency translation adjustments	78.0				(0.1)
Net income	78.0			78.0
Shares Outstanding at Jun. 30, 2019		52.8
Total stockholders’ equity at Jun. 30, 2019	1,283.7	$ 0.5	625.5	664.1	(6.4)
Shares Outstanding at Mar. 31, 2019		52.8
Total stockholders’ equity at Mar. 31, 2019	1,227.3	$ 0.5	613.2	621.0	(7.4)
Vesting of restricted stock units, shares		0.0
Vesting of restricted stock units, value	(1.3)		(1.3)
Stock-based compensation expense	13.6		13.6
Foreign currency translation adjustments	1.0				1.0
Net income	43.1			43.1
Shares Outstanding at Jun. 30, 2019		52.8
Total stockholders’ equity at Jun. 30, 2019	1,283.7	$ 0.5	625.5	664.1	(6.4)
Shares Outstanding at Dec. 31, 2019		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		0.2
Vesting of restricted stock units, value	(5.9)		(5.9)
Employee stock purchase plan, shares		0.2
Employee stock purchase plan, value	5.9		5.9
Stock Issued During Period, Value, Stock Options Exercised	17.1
Stock-based compensation expense	$ (27.9)		17.1
Stock Repurchased and Retired During Period, Shares	(0.8)
Stock Repurchased and Retired During Period, Value	$ (0.9)		(9.2)	(18.7)
Foreign currency translation adjustments	92.6				(0.9)
Net income	92.6			92.6
Shares Outstanding at Jun. 30, 2020		52.5
Total stockholders’ equity at Jun. 30, 2020	1,457.1	$ 0.5	645.9	818.6	(7.9)
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)
Vesting of restricted stock units, shares		0.1
Vesting of restricted stock units, value	(1.0)		(1.0)
Stock-based compensation expense	8.2		8.2
Foreign currency translation adjustments	1.6				1.6
Net income	48.8			48.8
Shares Outstanding at Jun. 30, 2020		52.5
Total stockholders’ equity at Jun. 30, 2020	$ 1,457.1	$ 0.5	$ 645.9	$ 818.6	$ (7.9)