Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net loss	$ (11,069,000)	$ (9,859,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Accretion on marketable securities	(247,000)
Depreciation and amortization expense	27,000	9,000
Stock-based compensation expense	663,000	1,181,000
Changes in operating assets and liabilities:
Restricted cash		(84,000)
Prepaid expenses and other current assets	(81,000)	(264,000)
Accounts payable	144,000	80,000
Accrued liabilities	(1,482,000)	1,105,000
Funding advance		500,000
Other liabilities	(4,000)	28,000
Net cash used in operating activities	(12,049,000)	(7,304,000)
Investing activities:
Purchases of property and equipment	(24,000)	(278,000)
Maturities of marketable securities	42,500,000
Purchases of marketable securities	(77,104,000)
Net cash used in investing activities	(34,628,000)	(278,000)
Financing activities:
Proceeds from public offering, net of issuance costs	46,816,000	89,938,000
Net cash provided by financing activities	46,816,000	89,938,000
Net increase in cash and cash equivalents	139,000	82,356,000
Cash and cash equivalents at beginning of period	7,042,000	53,349,000
Cash and cash equivalents at end of period	7,181,000	135,705,000
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable		8,000
Conversion of redeemable convertible preferred stock into common stock		$ 81,620,000
Issuance costs associated with public offering included in accounts payable	$ 231,000