Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities
Net income (loss)	$ (8,381)	$ 555
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Stock-based compensation	543	584
Non-cash interest expense	109	166
Non-cash change in fair value of PIPE Warrant liability	(2,648)	(8,815)
Amortization of premium and discount on investments	(51)
Changes in operating assets and liabilities:
Accounts receivable	(1,148)	455
Prepaid expenses and other current assets	559	241
Other noncurrent assets	(1,383)
Accounts payable	1,499	(1,390)
Accrued contract research	(580)	98
Other accrued liabilities	(860)	(778)
Other current liabilities	438
Deferred revenue	(493)	546
Deferred research and development reimbursements	117	(118)
Other non-current liabilities	592
Net cash used in operating activities	(11,687)	(8,456)
Investing activities
Purchases of property and equipment	(100)
Purchases of marketable securities	(7,152)
Proceeds from maturities and sales of marketable securities	15,000
Net cash provided by investing activities	7,748
Financing activities
Proceeds from issuance of common stock and warrants, net of issuance costs		7,512
Payment of principal of loan payable (Note 6)	(2,389)
Net cash (used in) provided by financing activities	(2,389)	7,512
Net decrease in cash and cash equivalents	(6,328)	(944)
Cash and cash equivalents at beginning of period	29,785	24,427
Cash and cash equivalents at end of period	23,457	23,483
Supplemental cash flow information
Cash paid for interest	368	507
Right-of-use asset obtained in exchange for operating lease liabilities	$ 1,225
Non-cash operating activity
Deferred offering costs accrued at period end		$ 212