CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (14,479,000)	$ (20,525,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	1,287,000	2,093,000
Amortization of financing issuance costs	281,000	0
Depreciation and amortization	132,000	144,000
Other	131,000	(139,000)
Changes in operating assets and liabilities:
Accounts receivable	(140,000)	(301,000)
Prepaid expenses and other assets	762,000	(944,000)
Accounts payable	(810,000)	661,000
Accrued and other liabilities	(2,412,000)	28,000
Net cash used in operating activities	(15,248,000)	(18,983,000)
Cash flows from investing activities:
Maturities of short-term investments	2,000,000	39,000,000
Proceeds from sale of property and equipment	1,000	0
Purchases of short-term investments	0	(28,726,000)
Purchases of property and equipment	0	(69,000)
Net cash provided by investing activities	2,001,000	10,205,000
Cash flows from financing activities:
Proceeds from the sale of common stock and warrants	19,754,000	426,000
Payment of issuance costs associated with the sale of common stock	(1,193,000)	(13,000)
Proceeds from issuance of notes payable	1,726,000	0
Payments of principal on notes payable	(1,333,000)	(333,000)
Proceeds from stock purchases under employee stock purchase plan	16,000	84,000
Proceeds from the exercise of stock options	13,000	15,000
Net cash provided by financing activities	18,983,000	179,000
Net increase (decrease) in cash and cash equivalents	5,736,000	(8,599,000)
Cash and cash equivalents at beginning of period	24,846,000	32,606,000
Cash and cash equivalents at end of period	30,582,000	24,007,000
Supplemental disclosure of cash flow information
Cash paid for interest	145,000	277,000
Supplemental disclosure of non-cash investing and financing activities
Amortization of public offering costs	30,000	1,000
Unpaid common stock issuance costs included in current liabilities	19,000	0
Change in unrealized gain on investments	$ 0	$ 14,000