Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (11,138)	$ (14,385)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	139	58
Net amortization of premiums and discounts on investments	(36)	(94)
Stock-based compensation expense	1,065	1,023
Gain on sale of property and equipment	(66)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	482	29
Other assets	337	691
Accounts payable	(461)	(25)
Operating lease liabilities	(211)	(173)
Accrued expenses and other current liabilities	(855)	(317)
Net cash used in operating activities	(10,744)	(13,193)
Cash flows from investing activities:
Purchases of property and equipment	(5)	(131)
Proceeds from sale of property and equipment	66
Purchases of investments	(1,756)	(21,284)
Proceeds from sales or maturities of investments	12,992	10,100
Net cash provided by (used in) investing activities	11,297	(11,315)
Cash flows from financing activities:
Proceeds from issuance of common stock and common warrants and pre-funded warrants, net of issuance costs	10,876	23,865
Proceeds from Paycheck Protection Program Loan	384
Proceeds from exercise of stock options		165
Net cash provided by financing activities	11,260	24,030
Net increase/(decrease) in cash, cash equivalents and restricted cash	11,813	(478)
Cash, cash equivalents and restricted cash at beginning of period	5,904	11,228	$ 11,228
Cash, cash equivalents and restricted cash at end of period	17,717	$ 10,750	$ 5,904
Supplemental disclosure of non-cash financing activities:
Issuance costs for issuance of common stock included in accounts payable and accrued expenses	$ 190