CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities:
Net loss	$ (30,098)	$ (27,824)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	57	48
Accretion and amortization on investments, net	196	416
Amortization of debt issuance costs/debt discounts	349	180
Gain on sales of equity investment		(1,233)
Stock-based compensation for services by non-employees	15	25
Stock-based compensation for employees and directors	1,692	1,794
Amortization of right-of-use assets	141	132
Changes in assets and liabilities:
Current and noncurrent assets	(7,293)	(3,757)
Current and noncurrent liabilities	967	(2,515)
Net cash used in operating activities	(33,974)	(32,734)
Cash flows from investing activities:
Purchases of property and equipment	(50)	(10)
Purchases of marketable securities	(18,104)	(25,122)
Proceeds from maturities of marketable securities	48,581	61,621
Proceeds from sales of equity investment		1,594
Net cash provided by investing activities	30,427	38,083
Cash flows from financing activities:
Proceeds from issuances of common stock from equity plans		17
Proceeds from issuances of common stock from at market offerings, net of paid issuance costs		16,234
Proceeds from exercise of warrants		12
Net cash provided by financing activities		16,263
Effect of exchange rates on cash, cash equivalents and restricted cash	1
Net change in cash, cash equivalents and restricted cash	(3,547)	21,612
Cash, cash equivalents and restricted cash at the beginning of the period	35,235	10,288
Cash, cash equivalents and restricted cash at the end of the period	$ 31,689	$ 31,900