Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (14,561)	$ (22,692)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	2,033	1,401
Depreciation expense	83	79
Non-cash interest expense	4	4
Non-cash lease expense	268	246
Changes in assets and liabilities:
Prepaid expenses and other current assets	1,105	(900)
Other assets		123
Accounts payable	(2,483)	216
Accrued expenses	(1,506)	(868)
Operating lease liabilities	(226)	(244)
Other liabilities		(1)
Net cash used in operating activities	(15,283)	(22,636)
Cash flows from investing activities:
Purchases of property and equipment		(101)
Net cash used in investing activities		(101)
Cash flows from financing activities:
Proceeds from the issuance of common stock, net of issuance costs	13,700	9,569
Proceeds from exercise of stock options	18	13
Proceeds from the issuance of stock through ESPP	27	49
Repayment of loan payable	(2,000)
Other	(16)	(14)
Net cash provided by financing activities	11,729	9,617
Net decrease in cash and cash equivalents	(3,554)	(13,120)
Cash and cash equivalents, beginning of period	30,007	61,643
Cash and cash equivalents, end of period	26,453	48,523
Supplemental disclosures:
Right-of-use assets obtained in exchange of operating lease obligations		992
Issuance costs included in accounts payable and accrued expenses	$ 42	$ 123