Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities:
Net loss	$ (5,725)	$ (5,169)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	128	149
Stock-based compensation	891	754
Noncash interest expense on loans	8	123
Revaluation of warrant liability	(3)	12
(Accretion) amortization of bond (discount) premium on marketable securities		(159)
Change in right-of-use asset	83
Changes in operating assets and liabilities:
Prepaid expenses and other assets	19	(974)
Operating lease liabilities	(144)
Accounts payable, accrued expenses and other liabilities	(1,475)	(2,419)
Net cash used in operating activities	(6,218)	(7,683)
Investing activities:
Maturities of marketable securities	3,500	18,179
Purchases of marketable securities		(29,219)
Net cash (used in) provided by investing activities	3,500	(11,040)
Financing activities:
Proceeds from exercise of common stock options		21
Proceeds from issuance of common stock, net	3,551	9,243
Capital lease payments	(2)
Capital lease payments		(3)
Repayments of loans payable, net	(5,045)	(3,167)
Net cash (used in) provided by financing activities	(1,496)	6,094
Net decrease in cash, cash equivalents and restricted cash	(4,214)	(12,629)
Cash, cash equivalents and restricted cash?beginning of period	33,614	34,195
Cash, cash equivalents and restricted cash?end of period	29,400	21,566
Supplemental disclosure of cash flow information:
Cash paid for interest	18	229
Fair value of common stock warrants issued to underwriters	$ 347	$ 347