Fair Value of Financial Assets and Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Fair Value, Assets Transfers
Fair value of assets transferred from Level 1 to Level 2	$ 0	$ 0
Fair value of assets transferred from Level 2 to Level 1	0	0
Fair value of asset transfer into level 3	0	0
Fair value of asset transfer into level 3	$ 0	$ 0
Number of securities in an unrealized loss position | security	17	7
Unrealized loss position	$ 107,753	$ 43,107
U.S. Treasury Notes
Assets - Fair Value
Short-term investments	282,139	196,644
Short-term investments
Amortized Cost	282,153	196,606
Gross Unrealized Gains	5	45
Gross Unrealized Losses	(19)	(7)
Cash equivalents | U.S. Treasury Notes
Assets - Fair Value
Short-term investments	72,695	10,192
Short-term investments
Amortized Cost	72,694	10,191
Gross Unrealized Gains	1	1
Short-term Investments | U.S. Treasury Notes
Assets - Fair Value
Short-term investments	209,444	186,452
Short-term investments
Amortized Cost	209,459	186,415
Gross Unrealized Gains	4	44
Gross Unrealized Losses	(19)	(7)
Fair Value | Recurring basis
Assets - Fair Value
Assets	305,291	222,061
Fair Value | Recurring basis | Money Market Funds
Assets - Fair Value
Restricted cash	210	210
Cash equivalents	22,942	25,207
Fair Value | Recurring basis | U.S. Treasury Notes
Assets - Fair Value
Cash equivalents	72,695	10,192
Short-term investments	209,444	186,452
Fair Value | Recurring basis | Level 1
Assets - Fair Value
Assets	23,152	25,417
Fair Value | Recurring basis | Level 1 | Money Market Funds
Assets - Fair Value
Restricted cash	210	210
Cash equivalents	22,942	25,207
Fair Value | Recurring basis | Level 2
Assets - Fair Value
Assets	282,139	196,644
Fair Value | Recurring basis | Level 2 | U.S. Treasury Notes
Assets - Fair Value
Cash equivalents	72,695	10,192
Short-term investments	$ 209,444	$ 186,452