Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 298,887	$ 553,439
Short-term investment securities	15,876	51,987
Accounts receivable, net	1,389
Prepaid research and development	11,929	5,231
Other current assets	2,884	1,083
Total current assets	330,965	611,740
Restricted cash	1,264	1,259
Long-term investment securities	35,533
Right of use assets	8,629	9,312
Leasehold interest, net	1,839	2,051
Equipment, net	600	481
Goodwill	799	799
Total assets	379,629	625,642
Current liabilities:
Accounts payable and accrued expenses	51,294	37,014
Other current liabilities	1,512	18,236
Loan payable - current portion	975	22,179
Lease liability - current portion	1,437	1,669
Accrued compensation	10,166	8,456
Total current liabilities	65,384	87,554
Deferred revenue, net of current portion	457	610
Loan payable - non-current	66,788	7,716
Lease liability - non-current	9,847	10,412
Total liabilities	142,476	106,292
Commitments and contingencies
Stockholders' equity:
Common stock, $0.001 par value per share (175,000,000 shares authorized, 143,292,043 and 140,617,606 shares issued, 143,250,734 and 140,576,297 shares outstanding at December 31, 2021 and December 31, 2020, respectively)	143	141
Additional paid-in capital	1,565,942	1,500,040
Treasury stock, at cost, 41,309 shares at December 31, 2021 and December 31, 2020	(234)	(234)
Accumulated deficit	(1,328,698)	(980,597)
Total stockholders' equity	237,153	519,350
Total liabilities and stockholders' equity	$ 379,629	$ 625,642