Stock-Based Compensation and Employee Benefit Plan - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Outstanding Options/RSUs, Number of Shares
Outstanding (in shares)	14,558,420
Granted (in shares)	743,705
Exercised (in shares)	(136,382)
Cancelled (in shares)	(111,693)
Outstanding (in shares)	15,054,050	14,558,420
Outstanding Options Weighted Average Exercise Price
Outstanding (in dollars per share)	$ 25.93
Granted (in dollars per share)	11.38
Exercised (in dollars per share)	4.23
Cancelled (in dollars per share)	25.44
Outstanding (in dollars per share)	$ 25.41	$ 25.93
Outstanding, remaining contractual life	6 years 7 months 13 days	6 years 9 months 11 days
Outstanding, aggregate intrinsic value	$ 4,686	$ 3,084
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Vested and expected to vest (in shares)	14,690,193
Exercisable (in shares)	8,555,962
Vested and expected to vest, weighted average exercise price (in dollars per share)	$ 25.56
Exercisable, weighted average exercise price (in dollars per share)	$ 28.18
Vested and expected to vest, remaining contractual life	6 years 6 months 22 days
Exercisable, remaining contractual life	4 years 11 months 19 days
Vested and expected to vest, aggregate intrinsic value	$ 4,645
Exercisable, aggregate intrinsic value	$ 3,586