CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 105,895	$ 181,133
Short-term investments	117,312	66,379
Unbilled revenue	750	750
Prepaid expenses and other current assets	4,625	3,800
Total current assets	228,582	252,062
Property and equipment, net	2,968	3,436
Right-of-use assets	3,468	3,970
Other assets	304	314
Total assets	235,322	259,782
Current liabilities:
Accounts payable	1,012	2,187
Accrued compensation and benefits	1,951	4,453
Less: Current portion of operating lease liability	2,715	2,608
Loan payable, current portion	7,437	1,183
Deferred revenue	3,366	4,541
Accrued expenses and other current liabilities	6,936	7,248
Total current liabilities	23,417	22,220
Operating lease liability, net of current portion	1,355	2,076
Loan payable, net of current portion	42,793	48,831
Total liabilities	67,565	73,127
Commitments and contingencies (Note 10)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized; no shares issued and outstanding as of March 31, 2020 and December 31, 2019, respectively.
Common stock, $0.0001 par value; 300,000,000 shares authorized; 89,035,096 and 88,817,741 shares issued and outstanding as of March 31, 2020 and December 31, 2019, respectively.	9	9
Additional paid-in capital	650,617	647,078
Accumulated deficit	(482,825)	(460,452)
Accumulated other comprehensive (loss) income	(44)	20
Total stockholders’ equity	167,757	186,655
Total liabilities and stockholders’ equity	$ 235,322	$ 259,782