Common Stock and Stockholders' Equity - Employee Stock Purchase Plan (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2015	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Stock Purchase Plan
Stock-based compensation		$ 21,928	$ 17,368	$ 40,243	$ 30,891
ESPP
Employee Stock Purchase Plan
Shares reserved for issuance under the plan (in shares)		832,492		832,492
Maximum offering period	27 months
Stock purchase price as a percentage of fair value (as a percent)	85.00%
Issuance of stock under employee stock purchase plan (in shares)		35,901	35,716
Remaining shares available for issuance under the plan (in shares)		519,366		519,366
Stock-based compensation		$ 500	$ 200	$ 900	$ 500
Unrecognized compensation cost		$ 800		$ 800
Period over which unrecognized compensation cost is expected to be recognized				4 months 24 days