Consolidated Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (8,063,000)	$ (3,986,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	597,000	567,000
Depreciation and amortization	16,000	15,000
Accretion on marketable securities	323,000	19,000
Changes in operating assets and liabilities:
Prepaid and other current assets	(1,763,000)	354,000
Other assets	81,000	233,000
Accounts payable, accrued liabilities and other liabilities	834,000	(1,443,000)
Net cash used in operating activities	(7,975,000)	(4,241,000)
Cash flows from investing activities:
Purchase of marketable securities	(75,911,000)	0
Sale of marketable securities	10,821,000	11,104,000
Purchases of property and equipment	0	(2,000)
Net cash (used in) provided by investing activities	(65,090,000)	11,102,000
Cash flows from financing activities:
Proceeds from exercise of options	24,000	0
Tax withholding payments on net share settlement equity awards	(184,000)	(148,000)
Net proceeds from issuance of common stock	85,457,000	0
Net cash provided by (used in) financing activities	85,297,000	(148,000)
Net increase in cash and cash equivalents	12,232,000	6,713,000
Cash and cash equivalents at beginning of period	16,512,000	14,032,000
Cash and cash equivalents at end of period	$ 28,744,000	$ 20,745,000