CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net loss	$ (23,546)	$ (24,621)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	343	372
Accretion related to marketable securities	(68)	(384)
Stock-based compensation	3,228	3,851
Changes in operating assets and liabilities:
Prepaid and other current assets	59	(313)
Operating lease right-of-use asset	331	292
Other assets	12	(50)
Accounts payable	331	640
Accrued and other liabilities	899	2,384
Operating lease liability	(428)	(375)
Net cash used in operating activities	(18,839)	(18,204)
Cash flows from investing activities
Purchases of marketable securities	(29,734)	(64,502)
Sales of marketable securities	1,009
Maturities of marketable securities	63,092	73,703
Purchases of property and equipment		(16)
Net cash provided by investing activities	34,367	9,185
Cash flows from financing activities
Proceeds from exercise of common stock options	23	6
Net cash provided by financing activities	23	6
Net increase (decrease) in cash and cash equivalents	15,551	(9,013)
Cash and cash equivalents at beginning of the period	5,154	39,196
Cash and cash equivalents at end of the period	$ 20,705	$ 30,183