Stockholders' Equity - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Options
Options outstanding, beginning balance (in shares)	5,799	6,266	7,959
Granted (in shares)	737	1,425	2,033
Exercised (in shares)	(1,683)	(1,523)	(3,120)
Cancelled or expired (in shares)	(521)	(369)	(606)
Options outstanding, ending balance (in shares)	4,332	5,799	6,266
Options vested and expected to vest	1,470	5,096	5,550
Options exercisable	2,280	2,901	3,278
Weighted Average Exercise Price
Options outstanding, beginning balance (in dollars per share)	$ 16.57	$ 12.13	$ 10.71
Granted (in dollars per share)	31.21	29.76	15.00
Exercised (in dollars per share)	12.69	11.12	10.70
Cancelled (in dollars per share)	23.27	14.76	10.03
Options outstanding, ending balance (in dollars per share)	19.78	16.57	12.13
Options vested and expected to vest (in dollars per share)	23.88	15.29	11.89
Options exercisable (in dollars per share)	$ 14.80	$ 12.03	$ 11.12
Weighted Average Remaining Contractual Term (in years)
Options outstanding	6 years 9 months 14 days	6 years 9 months 14 days	6 years 6 months 18 days
Options vested and expected to vest	8 years 2 months 8 days	6 years 5 months 26 days	6 years 3 months 10 days
Options exercisable	5 years 4 months 24 days	4 years 11 months 12 days	4 years 7 months 20 days
Aggregate Intrinsic Value
Options outstanding	$ 183,825	$ 119,064	$ 43,348
Options vested and expected to vest	56,382	110,934	39,521
Options exercisable	$ 108,128	$ 72,424	$ 25,367