Summary of Significant Accounting Policies - Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Assets fair value	$ 72,251	$ 57,920
Cash equivalents | Money Market Funds
Assets:
Assets fair value	28,548	4,847
Cash equivalents | Commercial Paper
Assets:
Assets fair value	6,098	26,964
Short-term Investments | Corporate Debt Securities
Assets:
Assets fair value	35,432	22,159
Short-term Investments | Asset-backed securities
Assets:
Assets fair value	2,173	3,950
Level 1
Assets:
Assets fair value	28,548	4,847
Level 1 | Cash equivalents | Money Market Funds
Assets:
Assets fair value	28,548	4,847
Level 2
Assets:
Assets fair value	43,703	53,073
Level 2 | Cash equivalents | Commercial Paper
Assets:
Assets fair value	6,098	26,964
Level 2 | Short-term Investments | Corporate Debt Securities
Assets:
Assets fair value	35,432	22,159
Level 2 | Short-term Investments | Asset-backed securities
Assets:
Assets fair value	$ 2,173	$ 3,950