Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 19,589	$ 66,923
Marketable securities	29,934
Inventories	2,990	2,352
Prepaid expenses and other current assets	3,270	1,448
Total current assets	55,783	70,723
Restricted cash	2,911	1,311
Property and equipment, net	1,631	1,841
Right-of-use lease asset	4,474	4,706
Other assets	3	1,543
Total assets	64,802	80,124
Current liabilities:
Accounts payable, net	2,719	4,547
Accrued expenses and other current liabilities	5,951	3,847
Lease liability	839	792
Total current liabilities	9,509	9,186
Loans payable, net	13,472
Leases, net of current portion	5,879	6,309
Total liabilities	28,860	15,495
Commitments and contingencies (Note 9)
Stockholders' equity:
Preferred stock-$0.001 par value; 5,000,000 shares authorized, none issued or outstanding at June 30, 2022 and December 31, 2021
Common stock-$0.001 par value; 200,000,000 shares authorized at June 30, 2022 and December 31, 2021; 165,681,085 and 165,520,007 shares issued and outstanding at June 30, 2022 and December 31, 2021, respectively	165	165
Additional paid-in capital	561,332	558,566
Subscription receivable	(23)
Accumulated deficit	(525,472)	(494,102)
Accumulated other comprehensive loss	(60)
Total stockholders' equity	35,942	64,629
Total liabilities and stockholders' equity	$ 64,802	$ 80,124