Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 471,514	$ 553,439
Short-term investment securities	52,334	51,987
Accounts receivable, net	771
Prepaid research and development	5,590	5,231
Other current assets	4,804	1,083
Total current assets	535,013	611,740
Restricted cash	1,260	1,259
Leasehold interest, net	1,998	2,051
Equipment, net	488	481
Right of use assets	9,141	9,312
Goodwill	799	799
Total assets	548,699	625,642
Current liabilities:
Accounts payable and accrued expenses	42,837	37,014
Other current liabilities	14,460	18,236
Loan payable - current portion	30,127	22,179
Lease liability - current portion	1,533	1,669
Accrued compensation	3,537	8,456
Total current liabilities	92,494	87,554
Deferred revenue, net of current portion	571	610
Loan payable - non-current		7,716
Lease liability - non-current	10,349	10,412
Total liabilities	103,414	106,292
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.001 par value per share (10,000,000 shares authorized, none issued and outstanding as of March 31, 2021 and December 31, 2020)	0	0
Common stock, $0.001 par value per share (150,000,000 shares authorized, 141,520,696 and 140,617,606 shares issued, 141,479,387 and 140,576,297 shares outstanding at March 31, 2021 and December 31, 2020, respectively)	142	141
Additional paid-in capital	1,516,602	1,500,040
Treasury stock, at cost, 41,309 shares at March 31, 2021 and December 31, 2020	(234)	(234)
Accumulated deficit	(1,071,225)	(980,597)
Total stockholders' equity	445,285	519,350
Total liabilities and stockholders' equity	$ 548,699	$ 625,642