Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (9,067)	$ (7,862)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	60	56
Amortization of debt discount		235
Net amortization of premiums and discounts on marketable securities	(42)
Stock-based compensation	60	36
Change in fair value of derivative liabilities		(308)
Loss on extinguishment of related party convertible promissory note		2,180
Changes in operating assets and liabilities:
Accounts receivable	11	37
Prepaid expenses and other current assets	229	(65)
Accounts payable	117	348
Accrued expenses	156	309
Deferred revenue		(131)
Net cash used in operating activities	(8,476)	(5,165)
CASH FLOWS FROM INVESTING ACTIVITIES:
Sales and maturities of marketable securities	11,800
Purchase of property and equipment		(47)
Net cash provided by (used in) investing activities	11,800	(47)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments of initial public offering costs		(44)
Repayment of convertible promissory note, related party		(4,000)
Proceeds from capital contribution		8,000
Net cash provided by financing activities		3,956
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	3,324	(1,256)
CASH AND CASH EQUIVALENTS–Beginning of period	5,618	4,180
CASH AND CASH EQUIVALENTS–End of period	$ 8,942	2,924
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Cash paid for interest		13
Purchase of property and equipment in accounts payable		9
Deferred offering costs in accounts payable and accrued expenses		573
Deferred offering costs reclassed from prepaid expenses and other current assets		$ 38