Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities:
Net loss	$ (4,226)	$ (8,063)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	760	597
Depreciation and amortization	7	16
Accretion on marketable securities	515	323
Changes in operating assets and liabilities:
Prepaid and other current assets	(969)	(1,763)
Other assets	57	81
Accounts payable, accrued liabilities and other liabilities	(1,786)	834
Net cash used in operating activities	(5,642)	(7,975)
Cash flows from investing activities:
Purchase of marketable securities	(26,546)	(75,911)
Sale of marketable securities	20,456	10,821
Net cash used in investing activities	(6,090)	(65,090)
Cash flows from financing activities:
Proceeds from exercise of options	0	24
Tax withholding payments on net share settlement equity awards	(168)	(184)
Net proceeds from issuance of common stock	0	85,457
Net cash (used in) provided by financing activities	(168)	85,297
Net (decrease) increase in cash and cash equivalents	(11,900)	12,232
Cash and cash equivalents at beginning of period	24,647	16,512
Cash and cash equivalents at end of period	$ 12,747	$ 28,744