Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands		Sep. 30, 2021	Dec. 31, 2020
Assets:
Investments, Fair Value		$ 206,267
Fair Value, Recurring
Assets:
Cash and cash equivalents, Amortized Cost		112,044
Cash and cash equivalents, Fair Value		112,044
Investments, Amortized Cost		206,279
Investments, Gross Unrealized Gains		12
Investments, Gross Unrealized Losses		(24)
Investments, Fair Value		206,267
Total assets measured at fair value, Amortized Cost		318,323	$ 386,200
Total assets measured at fair value, Gross Unrealized Gains		12
Total assets measured at fair value, Gross Unrealized Losses		(24)
Total assets measured at fair value, Fair Value		318,311	386,200
Fair Value, Recurring | Cash | Level 1
Assets:
Cash and cash equivalents, Amortized Cost		52,611	4,788
Cash and cash equivalents, Fair Value		52,611	4,788
Fair Value, Recurring | Money Market Funds | Level 1
Assets:
Cash and cash equivalents, Amortized Cost	[1]	51,183	381,412
Cash and cash equivalents, Fair Value	[1]	51,183	$ 381,412
Fair Value, Recurring | Commercial Paper | Level 2
Assets:
Cash and cash equivalents, Amortized Cost	[1]	8,250
Cash and cash equivalents, Fair Value	[1]	8,250
Fair Value, Recurring | U.S. Government Agency Securities | Level 2
Assets:
Investments, Amortized Cost		24,752
Investments, Gross Unrealized Gains		1
Investments, Fair Value		24,753
Fair Value, Recurring | U.S. Treasury Securities | Level 1
Assets:
Investments, Amortized Cost		43,390
Investments, Gross Unrealized Gains		11
Investments, Fair Value		43,401
Fair Value, Recurring | Corporate Debt | Level 2
Assets:
Investments, Amortized Cost		54,213
Investments, Gross Unrealized Losses		(16)
Investments, Fair Value		54,197
Fair Value, Recurring | Asset-backed Securities | Level 2
Assets:
Investments, Amortized Cost		13,958
Investments, Gross Unrealized Losses		(7)
Investments, Fair Value		13,951
Fair Value, Recurring | Commercial Paper, Not Included with Cash and Cash Equivalents | Level 2
Assets:
Investments, Amortized Cost		69,966
Investments, Gross Unrealized Losses		(1)
Investments, Fair Value		$ 69,965

[1] Included within cash and cash equivalents on the condensed balance sheets.