CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (18,978)	$ (7,712)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	82	68
Stock-based compensation	262	58
Non-cash interest expense	3,580	1,605
Change in fair value warrant liability	2,709	(130)
Change in fair value derivative liability	676	179
Changes in operating assets and liabilities:
Other receivable	(411)
Prepaid expenses and other assets	130	(67)
Accounts payable	558	(39)
Accrued expenses	1,182	204
Deferred rent	(5)	(1)
Net cash used in operating activities	(10,215)	(5,835)
Investing activities
Purchases of property and equipment	(31)	(204)
Net cash used in investing activities	(31)	(204)
Financing activities
Proceeds from issuance of redeemable convertible preferred stock, net	17,712
Proceeds from term loan, net	3,995
Payments of offering costs	(595)
Proceeds from exercise of stock options	53
Proceeds from exercise of warrants	16
Proceeds from convertible promissory notes, net		6,601
Net cash provided by financing activities	21,181	6,601
Net increase in cash and cash equivalents	10,935	562
Cash and cash equivalents at the beginning of the period	13,406	3,715
Cash and cash equivalents at the end of the period	24,341	4,277
Supplemental disclosure for cash flow
Cash paid for interest	161
Supplemental disclosure of cash flow information
Conversion of convertible promissory notes into redeemable convertible preferred stock	19,778
Issuance of warrants in conjunction with debt	2,822	1,046
Deferred offering costs included in accounts payable and accrued expenses	1,623
Warrant liability converted to redeemable convertible preferred stock upon the exercise of warrants	1,196
Accretion of redeemable convertible preferred stock	$ 95	50
Issuance of derivative in conjunction with debt		$ 1,309