CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 100,494	$ 181,133
Short-term investments	104,347	66,379
Unbilled revenue	750	750
Prepaid expenses and other current assets	6,035	3,800
Total current assets	211,626	252,062
Property and equipment, net	2,501	3,436
Right-of-use assets	2,945	3,970
Other assets	271	314
Total assets	217,343	259,782
Current liabilities:
Accounts payable	4,212	2,187
Accrued compensation and benefits	3,081	4,453
Current portion of operating lease liability	2,826	2,608
Loan payable, current portion	13,716	1,183
Deferred revenue	2,241	4,541
Accrued expenses and other current liabilities	7,574	7,248
Total current liabilities	33,650	22,220
Operating lease liability, net of current portion	608	2,076
Loan payable, net of current portion	36,735	48,831
Total liabilities	70,993	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 June 30, 2020 and December 31, 2019, respectively.
Common stock, $0.0001 par value; 300,000,000 shares authorized; 89,140,563 and 88,817,741 shares issued and outstanding as of June 30, 2020 and December 31, 2019, respectively.	9	9
Additional paid-in capital	653,805	647,078
Accumulated deficit	(507,781)	(460,452)
Accumulated other comprehensive income	317	20
Total stockholders' equity	146,350	186,655
Total liabilities and stockholders' equity	$ 217,343	$ 259,782