Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating Activities
Net loss	$ (4,426)	$ (1,253)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	42	4
Stock-based compensation expense	212	135
Non-cash interest expense		73
(Increase) decrease in
Prepaids and other current assets	63	122
Accounts payable	21	181
Accrued expenses and other current liabilities	101	73
Net cash used in operating activities	(3,987)	(665)
Investing Activities
Purchases of property and equipment	(98)	(39)
Purchases of other noncurrent assets	(64)
Purchases of short-term investments	(3,639)
Net cash used in investing activities	(3,801)	(39)
Financing Activities
Proceeds from the issuance of convertible promissory notes		1,299
Proceeds from the issuance of related party convertible promissory notes		1,000
Issuance of common stock, net	10
Net cash provided by financing activities	10	2,299
Net (decrease) increase in cash and cash equivalents	(7,778)	1,595
Cash and cash equivalents at beginning of period	49,591
Cash and cash equivalents at end of period	$ 41,813	3,518
Supplemental Disclosures of Non-Cash Investing and Financing Activities
Conversion of preferred units to preferred stock		1,306
Unpaid deferred offering costs		$ 287