Equity Incentive Plans - Summary of Stock Option Activity Under 2006 and 2016 Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Options Outstanding
Beginning balance (in shares)	1,503,247	2,094,137
Options granted (in shares)		20,010
Options exercised (in shares)	(264,800)	(540,307)
Options forfeited (in shares)	(16,826)	(70,593)
Ending balance (in shares)	1,221,621	1,503,247	2,094,137
Options exercisable (in shares)	941,215
Options vested and expected to vest (in shares)	1,210,815
Weighted- Average Exercise Price Per Share
Beginning Balance (in USD per share)	$ 27.40	$ 23.20
Options granted (in USD per share)		82.77
Options exercised (in USD per share)	11.21	9.59
Options forfeited (in USD per share)	68.32	54.54
Ending Balance (in USD per share)	30.35	$ 27.40	$ 23.20
Options exercisable (in USD per share)	23.59
Options vested and expected to vest (in USD per share)	$ 30.07
Weighted- Average Remaining Contractual Life (years)
Beginning Balance	6 years 4 months 20 days	6 years 5 months 4 days	7 years 7 days
Ending Balance	6 years 4 months 20 days	6 years 5 months 4 days	7 years 7 days
Options exercisable	6 years 18 days
Options vested and expected to vest	6 years 4 months 17 days
Aggregate Intrinsic Value (in thousands)
Beginning Balance (in USD)	$ 62,401	$ 97,976
Ending Balance (in USD)	62,595	$ 62,401	$ 97,976
Options exercisable (in USD)	54,482
Options vested and expected to vest (in USD)	$ 62,368