Summary of Significant Accounting Policies - Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets:
Assets fair value	$ 58,345	$ 102,230
Cash equivalents | Money Market Funds
Assets:
Assets fair value	29,170	33,535
Cash equivalents | Commercial Paper
Assets:
Assets fair value		15,746
Cash equivalents | Corporate Debt Securities
Assets:
Assets fair value		1,351
Short-term Investments | Corporate Debt Securities
Assets:
Assets fair value	24,565	38,672
Short-term Investments | U.S. Government Agency Bonds
Assets:
Assets fair value		4,642
Short-term Investments | Asset-backed securities
Assets:
Assets fair value	4,610	8,284
Level 1
Assets:
Assets fair value	29,170	33,535
Level 1 | Cash equivalents | Money Market Funds
Assets:
Assets fair value	29,170	33,535
Level 2
Assets:
Assets fair value	29,175	68,695
Level 2 | Cash equivalents | Commercial Paper
Assets:
Assets fair value		15,746
Level 2 | Cash equivalents | Corporate Debt Securities
Assets:
Assets fair value		1,351
Level 2 | Short-term Investments | Corporate Debt Securities
Assets:
Assets fair value	24,565	38,672
Level 2 | Short-term Investments | U.S. Government Agency Bonds
Assets:
Assets fair value		4,642
Level 2 | Short-term Investments | Asset-backed securities
Assets:
Assets fair value	$ 4,610	$ 8,284