BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 34,871	$ 9,925
Restricted cash	364	363
Marketable securities	148,851	186,350
Interest and other receivables	1,763	722
Prepaid and other current assets	1,357	2,497
Total current assets	187,206	199,857
Noncurrent marketable securities	28,651	63,387
Property and equipment, net	650	658
Operating leases, right-of-use assets	4,727	5,295
Deposits and other assets	4,800	1,531
Total assets	226,034	270,728
Current liabilities:
Accounts payable	6,687	6,919
Accrued compensation and benefits	8,099	8,218
Operating lease liabilities	901	878
Accrued liabilities	29,834	14,925
Total current liabilities	45,521	30,940
Noncurrent operating lease liabilities	4,267	4,799
Noncurrent debt	49,830	24,042
Total liabilities	99,618	59,781
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.001 par value; 3,000,000 shares authorized; no shares issued and outstanding at December 31, 2021 and 2020
Common stock, $0.001 par value; 675,000,000 and 450,000,000 shares authorized at December 31, 2021 and 2020, respectively; 323,731,591 and 310,566,853 shares issued and outstanding at December 31, 2021 and 2020, respectively	324	310
Additional paid-in capital	1,398,006	1,366,188
Accumulated deficit	(1,271,741)	(1,155,629)
Accumulated other comprehensive (loss) gain	(173)	78
Total stockholders' equity	126,416	210,947
Total liabilities and stockholders' equity	$ 226,034	$ 270,728