Summary of Significant Accounting Policies - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Investments:
Total investments	$ 31,295	$ 43,844
Recurring basis
Cash equivalents:
Money market funds	164,052	179,389
Total cash equivalents	164,052	179,389
Investments:
Commercial paper	13,296	13,275
Corporate bonds		6,540
U.S. government securities	27,978	24,029
Total investments	41,274	43,844
Total cash equivalents and investments	205,326	223,233
Level 1 | Recurring basis
Cash equivalents:
Money market funds	164,052	179,389
Total cash equivalents	164,052	179,389
Investments:
Commercial paper	0	0
Corporate bonds		0
U.S. government securities	27,978	24,029
Total investments	27,978	24,029
Total cash equivalents and investments	192,030	203,418
Level 2 | Recurring basis
Cash equivalents:
Money market funds	0	0
Total cash equivalents	0	0
Investments:
Commercial paper	13,296	13,275
Corporate bonds		6,540
U.S. government securities	0	0
Total investments	13,296	19,815
Total cash equivalents and investments	13,296	19,815
Level 3 | Recurring basis
Cash equivalents:
Money market funds	0	0
Total cash equivalents	0	0
Investments:
Commercial paper	0	0
Corporate bonds		0
U.S. government securities	0	0
Total investments	0	0
Total cash equivalents and investments	$ 0	$ 0