Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 181,133	$ 78,768
Short-term investments	66,379	89,321
Accounts receivable		85
Unbilled revenue	750	5,000
Prepaid expenses and other current assets	3,800	3,197
Total current assets	252,062	176,371
Property and equipment, net	3,436	5,611
Right-of-use assets	3,970
Other assets	314	1,350
Total assets	259,782	183,332
Current liabilities:
Accounts payable	2,187	1,148
Accrued compensation and benefits	4,453	2,723
Uncharged license fees		1,000
Current portion of operating lease liability	2,608
Loan payable, current portion	1,183
Deferred revenue	4,541
Accrued expenses and other current liabilities	7,248	12,857
Total current liabilities	22,220	17,728
Operating lease liability, net of current portion	2,076
Loan payable, net of current portion	48,831	49,209
Other long-term liabilities		582
Total liabilities	73,127	67,519
Commitments and contingencies (Note 17)
Stockholders' equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized; no shares issued and outstanding as of December 31, 2019 and December 31, 2018, respectively.
Common stock, $0.0001 par value; 300,000,000 shares authorized; 88,817,741 and 62,516,627 shares issued and outstanding as of December 31, 2019 and December 31, 2018, respectively.	9	6
Additional paid-in capital	647,078	481,357
Accumulated deficit	(460,452)	(365,512)
Accumulated other comprehensive income (loss)	20	(38)
Total stockholders' equity	186,655	115,813
Total liabilities and stockholders' equity	$ 259,782	$ 183,332