Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 22,221	$ 28,864
Short-term debt securities	66,594	99,976
Accounts receivable, net	2,576
Inventories	2,612	93
Prepaid expenses and other current assets	9,361	8,873
Total current assets	103,364	137,806
Long-term debt securities	17,262
Property and equipment, net	613	709
Operating lease right-of-use assets	653	1,176
Other assets	4,510	3,903
Total assets	126,402	143,594
Current liabilities:
Accounts payable	7,765	4,640
Accrued liabilities	13,699	11,405
Current portion of operating lease liabilities	628	582
Current portion of long-term debt, net	7,809
Total current liabilities	29,901	16,627
Long-term debt, net	23,986	31,194
Operating lease liabilities	116	738
Total liabilities	54,003	48,559
Commitments and contingencies (Note 13)
Stockholders’ equity:
Common stock, $0.001 par value, 200,000,000 shares authorized as of December 31, 2021 and 2020; 34,568,821 and 33,878,486 shares issued and outstanding as of December 31, 2021 and 2020, respectively	35	34
Additional paid-in capital	412,930	401,509
Accumulated other comprehensive loss	(149)	(8)
Accumulated deficit	(340,417)	(306,500)
Total stockholders’ equity	72,399	95,035
Total liabilities and stockholders’ equity	$ 126,402	$ 143,594