Share-Based Compensation - Restricted Stock Units (Details) - Restricted stock units $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Number of shares
Outstanding, beginning balance | shares	707
Granted | shares	517
Released | shares	(166)
Cancelled/Forfeited | shares	(25)
Outstanding, ending balance | shares	1,033
Exercisable, ending balance | shares	4
Vested and expected to vest | shares	1,033
Weighted Average Share Price on Date of Release | $ / shares	$ 35.69
Weighted Average Fair Value
Outstanding, beginning balance | $ / shares	29.23
Granted | $ / shares	33.77
Released | $ / shares	28.78
Cancelled/Forfeited | $ / shares	32.15
Outstanding, ending balance | $ / shares	$ 31.50
Aggregate Intrinsic Value [Abstract]
Aggregate intrinsic value, outstanding | $	$ 26,732
Granted | $	17,444
Released | $	5,914
Cancelled/Forfeited | $	1,110
Aggregate intrinsic value, outstanding | $	46,384
Exercisable, ending balance | $	140
Vested and expected to vest | $	$ 46,384