Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets
Cash and cash equivalents	$ 55,611	$ 82,647
Investment securities, available-for-sale	47,651	32,720
Inventory	1,815	1,780
Other current assets	1,865	2,283
Total current assets	106,942	119,430
Property and equipment, net	3,248	3,026
Operating lease right-of-use asset	5,368	5,577
Restricted cash	1,092	1,092
Intangible assets, net	105	115
Other assets	1,014	985
Total assets	117,769	130,225
Current liabilities
Accounts payable	1,919	3,584
Accrued liabilities	1,288	1,170
Contract liabilities	4,915	5,265
Other current liabilities	474	1,181
Current portion of long-term debt	98	392
Current portion of operating lease liability	686	849
Current portion of finance lease obligations	24	21
Total current liabilities	9,404	12,462
Operating lease liability, net of current portion	4,882	4,983
Finance lease obligations, net of current portion	15	26
Total liabilities	14,301	17,471
Shareholders' equity
Preferred stock, par value $0.001; 25,000 shares authorized; no and     no shares issued and outstanding
Common stock, par value $0.001; 210,000 shares authorized;     164,887 and 164,363 shares issued and outstanding at March 31,     2022 and December 31, 2021, respectively	165	164
Additional paid-in capital	746,028	742,042
Accumulated other comprehensive loss	(124)	(19)
Accumulated deficit	(642,601)	(629,433)
Total shareholders' equity	103,468	112,754
Total liabilities and shareholders' equity	$ 117,769	$ 130,225