Stock-Based Awards - Restricted Stock Units (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Additional Information
Compensation expense recognized	$ 65,830	$ 54,699	$ 43,081
Restricted stock units
Number of Shares
Number of shares, outstanding at beginning of period (in shares)	3,254
Number of shares, granted (in shares)	1,938
Number of shares, forfeited (in shares)	(367)
Number of shares, vested (in shares)	(1,035)
Number of shares, outstanding at period end (in share)	3,790	3,254
Weighted Average Grant Date Fair Value
Weighted average grant date fair value, outstanding at beginning of period (in usd per share)	$ 36.35
Weighted average grant date fair value, granted (in usd per share)	37.99
Weighted average grant date fair value, forfeited (in usd per share)	36.04
Weighted average grant date fair value, vested (in usd per share)	36.34
Weighted average grant date fair value, outstanding at period end (in usd per share)	$ 37.22	$ 36.35
Additional Information
Compensation expense recognized	$ 44,100	$ 31,900	$ 15,000
Unrecognized compensation expense related to nonvested restricted stock units	$ 105,700
Unrecognized compensation expense, weighted-average period of recognition		2 years 8 months 23 days