BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 100,056	$ 115,069
Receivables	5,006	4,665
Prepaid expenses and other current assets	7,648	10,855
Total current assets	112,710	130,589
Property and equipment, net	11,090	10,231
Right of use asset	4,357	4,650
Deposits	130	130
Other non-current assets	185	745
Total assets	128,472	146,345
Current liabilities:
Accounts payable	4,190	960
Accrued expenses	14,012	16,589
Lease liability - current portion	759	819
Total current liabilities	18,961	18,368
Lease liability - noncurrent portion	3,870	3,995
Total liabilities	22,831	22,363
Commitments and contingencies (Note 7)
Preferred stock, $0.001 par value, 30,000,000 shares authorized
Stockholders' equity:
Common stock, $0.001 par value; 250,000,000 shares authorized; 215,257,674 and 214,591,906 shares issued and outstanding at March 31, 2021 and December 31, 2020, respectively	215	215
Additional paid-in capital	891,081	887,868
Accumulated deficit	(785,655)	(764,101)
Total stockholders' equity	105,641	123,982
Total liabilities and stockholders' equity	$ 128,472	$ 146,345