Share-Based Compensation - Restricted Stock Units (Details) - Restricted stock units $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Number of shares
Outstanding, beginning balance | shares	707
Granted | shares	523
Released | shares	(279)
Cancelled/Forfeited | shares	(34)
Outstanding, ending balance | shares	917
Vested and expected to vest | shares	917
Weighted Average Share Price on Date of Release | $ / shares	$ 37.66
Weighted Average Fair Value
Outstanding, beginning balance | $ / shares	29.23
Granted | $ / shares	33.83
Released | $ / shares	28.92
Cancelled/Forfeited | $ / shares	32.58
Outstanding, ending balance | $ / shares	$ 31.82
Aggregate Intrinsic Value [Abstract]
Aggregate intrinsic value, outstanding | $	$ 26,732
Granted | $	17,704
Released | $	10,519
Cancelled/Forfeited | $	844
Aggregate intrinsic value, outstanding | $	22,605
Vested and expected to vest | $	$ 22,605