CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net loss	$ (23,330)	$ (26,615)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	1,749	2,637
Accretion of investment discounts and depreciation	(70)	9
Amortization of debt discount and debt issuance costs	116	192
Changes in operating assets and liabilities:
Prepaids and other assets	(294)	1,063
Accounts payable	(602)	(304)
Accrued clinical expense	21	(267)
Accrued compensation	42	(497)
Other accrued liabilities	183	(622)
Net cash used in operating activities	(22,185)	(24,404)
Cash flows from investing activities
Purchases of marketable securities	(20,035)
Sale and maturities of marketable securities	3,750	4,780
Net cash (used in) provided by investing activities	(16,285)	4,780
Cash flows from financing activities
Proceeds from notes payable, net of issuance cost	5,453
Principal payments on notes payable	(7,500)
Proceeds from issuance of convertible preferred stock offering, net	12,533
Proceeds from issuance of common stock, net	32,022
Proceeds from issuance of common stock through controlled equity offering facilities, net	464	6,040
Proceeds from exercise of stock options and stock purchase rights	63	303
Net cash provided by financing activities	43,035	6,343
Net increase (decrease) in cash and cash equivalents	4,565	(13,281)
Cash, cash equivalents and restricted cash at beginning of period	13,696	26,977
Cash, cash equivalents and restricted cash at end of period	18,261	13,696
Supplemental disclosure of cash flow information
Interest paid	695	790
Supplemental disclosure of non-cash investing and financing activities
Conversion of preferred stock to common stock	21,762
Right-of-use asset obtained in exchange for lease obligation	$ 1,362
Commitment shares issued as cost of equity financing		448
Legal expenses accrued as cost of equity financing, net of adjustments		$ 39