Share-Based Compensation - Option Activity (Details) - Employee stock options $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Number of Shares
Outstanding, beginning balance | shares	536
Exercised | shares	(80)
Forfeited | shares	(88)
Outstanding, ending balance | shares	368
Exercisable, ending balance | shares	368
Vested and expected to vest | shares	368
Weighted Average Exercise Price
Outstanding, beginning balance	$ 10.04
Exercised	9.74
Forfeited	9.93
Outstanding, ending balance	10.13
Exercisable, ending balance	10.13
Vested and expected to vest	10.13
Weighted Average Share Price on Date of Exercise	32.95
Weighted Average Fair Value [Abstract]
Outstanding, beginning balance	5.19
Exercised	4.90
Forfeited	5.10
Outstanding, ending balance	$ 5.27
Weighted Average Remaining Contractual Life
Outstanding, ending balance	5 years 1 month 13 days
Exercisable, ending balance	5 years 1 month 13 days
Vested and expected to vest	5 years 1 month 13 days
Aggregate Intrinsic Value
Aggregate intrinsic value, beginning balance | $	$ 14,888
Exercised | $	1,847
Forfeited | $	3,083
Aggregate intrinsic value, ending balance | $	12,802
Exercisable, ending balance | $	12,802
Vested and expected to vest | $	$ 12,802