Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities
Net income (loss)	$ 555	$ (8,988)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Stock-based compensation	584	583
Non-cash interest expense	166	111
Non-cash change in fair value of PIPE Warrant liability	(8,815)	1,465
Non-cash charge for Settlement Warrants (Note 9)		42
Amortization of premium and discount on investments		5
Changes in operating assets and liabilities:
Accounts receivable	455	(198)
Prepaid expenses and other current assets	241	249
Other noncurrent assets		4
Accounts payable	(1,390)	944
Accrued contract research	98	(984)
Other accrued liabilities	(778)	(496)
Deferred revenue	546	1,019
Deferred research and development reimbursements	(118)	(274)
Net cash used in operating activities	(8,456)	(6,518)
Investing activities
Purchases of marketable securities		(6,801)
Proceeds from maturities and sales of marketable securities		14,537
Net cash provided by investing activities		7,736
Financing activities
Proceeds from issuance of common stock, net of issuance costs	7,512	518
Proceeds from issuance of stock for stock-based compensation arrangements		15
Payment of end-of-term loan costs (Note 6)		(540)
Net cash provided by (used in) financing activities	7,512	(7)
Net (decrease) increase in cash and cash equivalents	(944)	1,211
Cash and cash equivalents at beginning of period	24,427	14,949
Cash and cash equivalents at end of period	23,483	16,160
Supplemental cash flow information
Cash paid for interest	507	509
Non-cash operating activity
Increase to deferred revenue due to adoption of ASC Topic 606 - transition adjustment on January 1, 2018		$ 2,711
Deferred offering costs accrued at period end	$ 212