Fair Value of Financial Assets and Liabilities - (Details) - Recurring - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Money market funds, included in cash and cash equivalents	$ 109,012	$ 34,896
Marketable securities:
U.S. Treasury obligations	26,048	121,140
Total assets	135,060	156,036
Level 1
Assets:
Money market funds, included in cash and cash equivalents	109,012	34,896
Marketable securities:
U.S. Treasury obligations	26,048	121,140
Total assets	$ 135,060	$ 156,036