Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (17,533)	$ (12,879)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	145	114
Purchase net discount (premium) on marketable securities	401	(40)
Net (accretion of discount) amortization of premium on marketable securities	(107)	80
Stock-based compensation	1,831	1,066
Research and development services settled with stock	41
Other, net	(20)	(13)
Changes in operating assets and liabilities:
Accounts receivable-grant	(1,203)	2
Prepaid expenses and other assets	(573)	29
Accounts payable	579	340
Deferred revenue	(20)
Accrued and other liabilities	(32)	(73)
Net cash used in operating activities	(16,491)	(11,374)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(118)	(317)
Purchases of marketable securities	(26,250)	(37,780)
Proceeds from maturities of marketable securities	11,870	17,010
Net cash used in investing activities	(14,498)	(21,087)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of common stock in public offering, net of offering costs	37,690	11,551
Proceeds from employee stock plan purchases and stock option exercises	1,061	96
Net cash provided by financing activities	38,751	11,647
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	7,762	(20,814)
CASH AND CASH EQUIVALENTS
Beginning of period	12,817	47,748
End of period	$ 20,579	$ 26,934