Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Assets:
Aggregate estimated fair value	$ 111,977	$ 135,457
Level 1 to level 2	0	0
Level 2 to level 1	0	0
Transfers into level 3	0	0
Transfers out of level 3	0	0
U.S. Treasury obligations
Assets:
Aggregate estimated fair value	111,977	135,457
Fair value on a recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial liabilities	0	0
Assets:
Total assets	218,784	236,784
Fair value on a recurring basis | Money market funds
Assets:
Assets included in cash and cash equivalents	106,807	91,332
Fair value on a recurring basis | U.S. Treasury obligations
Assets:
Assets included in cash and cash equivalents		9,995
Aggregate estimated fair value	111,977	135,457
Fair value on a recurring basis | Level 1
Assets:
Total assets	106,807	91,332
Fair value on a recurring basis | Level 1 | Money market funds
Assets:
Assets included in cash and cash equivalents	106,807	91,332
Fair value on a recurring basis | Level 2
Assets:
Total assets	111,977	145,452
Fair value on a recurring basis | Level 2 | U.S. Treasury obligations
Assets:
Assets included in cash and cash equivalents		9,995
Aggregate estimated fair value	$ 111,977	$ 135,457