Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (3,986)	$ (4,365)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	567	547
Depreciation and amortization	15	17
Accretion on marketable securities	19	82
Changes in operating assets and liabilities:
Prepaid and other current assets	354	(223)
Other assets	233	91
Accounts payable, accrued liabilities and other liabilities	(1,443)	(1,635)
Net cash used in operating activities	(4,241)	(5,486)
Cash flows from investing activities:
Purchase of marketable securities	0	(16,264)
Sale of marketable securities	11,104	25,005
Acquisition of property and equipment	(2)	0
Net cash provided by investing activities	11,102	8,741
Cash flows from financing activities:
Tax withholding payments on net share settlement equity awards	(148)	(130)
Net proceeds from issuance of common stock	0	1,000
Net cash (used in) provided by financing activities	(148)	870
Net increase in cash and cash equivalents	6,713	4,125
Cash and cash equivalents at beginning of period	14,032	10,299
Cash and cash equivalents at end of period	$ 20,745	$ 14,424