Stock-Based Compensation - Summary of Stock Options (Details) - Options to purchase common stock - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2019
Shares
Options outstanding at beginning of period (in shares)	5,463
Granted (in shares)	925
Exercised (in shares)	(341)
Canceled (in shares)	(454)
Expired (in shares)	(429)
Options outstanding at end of period (in shares)	5,164
Options exercisable at end of period (in shares)	2,957
Weighted- Average Exercise Price (in dollars per share)
Options outstanding at the beginning of the period (in dollars per share)	$ 36.88
Granted (in dollars per share)	19.34
Exercised (in dollars per share)	8.40
Canceled (in dollars per share)	34.23
Expired (in dollars per share)	39.66
Options outstanding at the end of the period (in dollars per share)	35.63
Options exercisable at the end of the period (in dollars per share)	$ 40.16
Weighted- Average Contractual Life (in years)
Options outstanding at the end of period	7 years 1 month 17 days
Options exercisable at the end of period	5 years 10 months 9 days
Aggregate Intrinsic Value
Options outstanding at the end of the period (in dollars)	$ 9,593
Options exercisable at the end of the period (in dollars)	$ 4,252