Stockholders' Equity - Summary of Stock Option Activity and Weighted Average Exercise Prices (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Options
Options outstanding, beginning balance (in shares)	7,959	7,769	9,144
Granted (in shares)	2,033	2,042	635
Exercised (in shares)	(3,120)	(854)	(325)
Cancelled or expired (in shares)	(606)	(998)	(1,685)
Options outstanding, ending balance (in shares)	6,266	7,959	7,769
Options vested and expected to vest	5,550	7,163	7,348
Options exercisable	3,278	5,163	5,580
Weighted Average Exercise Price
Options outstanding, beginning balance (in dollars per share)	$ 10.71	$ 10.88	$ 11.05
Granted (in dollars per share)	15.00	9.87	7.32
Exercised (in dollars per share)	10.70	8.80	5.66
Cancelled (in dollars per share)	10.03	11.98	11.49
Options outstanding, ending balance (in dollars per share)	12.13	10.71	10.88
Options vested and expected to vest (in dollars per share)	11.89	10.75	11.00
Options exercisable (in dollars per share)	$ 11.12	$ 11.17	$ 11.31
Weighted Average Remaining Contractual Term (in years)
Options outstanding	6 years 6 months 18 days	5 years 10 months 6 days	6 years 18 days
Options vested and expected to vest	6 years 3 months 11 days	5 years 5 months 27 days	5 years 10 months 24 days
Options exercisable	4 years 7 months 21 days	4 years 6 months	5 years 3 months 7 days
Aggregate Intrinsic Value
Options outstanding	$ 43,348	$ 14,881	$ 2,641
Options vested and expected to vest	39,521	13,197	2,529
Options exercisable	$ 25,367	$ 8,648	$ 2,347