CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (41,873)	$ (32,703)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	3,970	3,679
Non-cash interest expense	340	376
Depreciation and amortization	288	281
Amortization of premiums and discounts on available-for-sale securities	(432)	(416)
Changes in operating assets and liabilities:
Accounts receivable	(84)	1,432
Prepaid expenses and other assets	126	51
Accounts payable	525	(335)
Accrued and other liabilities	1,084	791
Net cash used in operating activities	(36,056)	(26,844)
Cash flows from investing activities:
Purchases of short-term investments	(32,690)	(62,462)
Maturities of short-term investments	61,000	33,000
Purchases of property and equipment	(84)	(445)
Net cash provided by (used in) investing activities	28,226	(29,907)
Cash flows from financing activities:
Payments of principal on note payable	(2,333)	0
Proceeds from the sale of common stock	2,283	44,529
Payment of issuance costs associated with the sale of common stock	(77)	(3,037)
Proceeds from stock purchases under employee stock purchase plan	110	242
Proceeds from the exercise of stock options	87	182
Net cash provided by financing activities	70	41,916
Net decrease in cash and cash equivalents	(7,760)	(14,835)
Cash and cash equivalents at beginning of period	32,606	47,441
Cash and cash equivalents at end of period	24,846	32,606
Supplemental disclosure of cash flow information
Cash paid for interest	511	489
Change in unrealized gain (loss) on investments	3	(3)
Supplemental disclosure of non-cash investing and financing activities
Change in unrealized gain (loss) on investments	3	(3)
Amortization of public offering costs	$ 3	$ 55