CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (8,044)	$ (11,629)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	664	1,018
Implementation of ASC 842 and other non-cash lease expenses	75
Non-cash interest expense	63	94
Depreciation and amortization	68	73
Loss on sale of equipment	11	0
Amortization of premiums and discounts on available-for-sale securities	(1)	(182)
Changes in operating assets and liabilities:
Accounts receivable	104	18
Prepaid expenses and other assets	436	(298)
Accounts payable	410	(54)
Accrued and other liabilities	(2,245)	(849)
Net cash used in operating activities	(8,459)	(11,809)
Cash flows from investing activities:
Purchases of short-term investments	0	(23,783)
Maturities of short-term investments	2,000	21,000
Proceeds from sale of property and equipment	1	0
Purchases of property and equipment	0	(37)
Net cash provided by (used in) investing activities	2,001	(2,820)
Cash flows from financing activities:
Proceeds from the sale of common stock and warrants	19,754	138
Payment of issuance costs associated with the sale of common stock	(1,068)	(4)
Payments of principal on note payable	(1,000)	0
Proceeds from stock purchases under employee stock purchase plan	16	84
Proceeds from the exercise of stock options	13	0
Net cash provided by financing activities	17,715	218
Net increase (decrease) in cash and cash equivalents	11,257	(14,411)
Cash and cash equivalents at beginning of period	24,846	32,606
Cash and cash equivalents at end of period	36,103	18,195
Supplemental disclosure of cash flow information
Cash paid for interest	61	136
Supplemental disclosure of non-cash investing and financing activities
Amortization of public offering costs	30	1
Change in unrealized gain on investments	$ 0	$ 5