Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net loss	$ (14,399)	$ (12,611)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	1,047	2,281
Depreciation and amortization	50	208
Gain on disposal of assets	0	(1,429)
Accretion on marketable securities	172	197
Changes in operating assets and liabilities:
Prepaid and other current assets	(30)	210
Other assets	272	182
Accounts payable, accrued liabilities and other liabilities	(1,774)	(5,982)
Net cash used in operating activities	(14,662)	(16,944)
Cash flows from investing activities:
Purchase of marketable securities	(32,312)	(60,191)
Sale of marketable securities	48,441	54,134
Proceeds from CFC device sale	0	2,550
Acquisition of property and equipment	0	(134)
Net cash provided by (used in) investing activities	16,129	(3,641)
Cash flows from financing activities:
Proceeds from exercise of options	0	355
Tax withholding payments on net share settlement equity awards	(130)	(403)
Net proceeds from issuance of common stock	1,038	998
Repayment of notes payable	0	(159)
Net cash provided by financing activities	908	791
Net increase (decrease) in cash, cash equivalents and restricted cash	2,375	(19,794)
Cash, cash equivalents and restricted cash at beginning of period	10,299	34,168
Cash and cash equivalents at end of period	12,674	14,374
Cash paid during the period for:
Interest	$ 0	$ 5