CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net loss	$ (11,643)	$ (14,301)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	186	219
Accretion related to marketable securities	(170)	(44)
Stock-based compensation	1,953	1,801
Other	119	(115)
Changes in operating assets and liabilities:
Prepaid and other current assets	(205)	(53)
Other assets	(51)	(194)
Accounts payable	266	45
Accrued and other liabilities	555	1,597
Net cash used in operating activities	(8,990)	(11,045)
Cash flows from investing activities
Purchases of marketable securities	(29,903)	(15,797)
Maturities of marketable securities	38,688	19,423
Purchase of property and equipment	(16)	(6)
Net cash provided by investing activities	8,769	3,620
Cash flows from financing activities
Proceeds from issuance of common stock, net (includes $30,850 in aggregate gross proceeds from related parties for the three months ended March 31, 2018		64,877
Proceeds from exercise of common stock options	1	7
Net cash provided by financing activities	1	64,884
Net increase (decrease) in cash and cash equivalents	(220)	57,459
Cash and cash equivalents at beginning of the period	39,196	45,106
Cash and cash equivalents at end of the period	38,976	$ 102,565
Supplemental disclosures of cash flow information
Purchases of property and equipment incurred but not paid	$ 16