Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (6,247)	$ (4,547)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	52	29
Purchase premium on marketable securities	(55)	(16)
Amortization of premium on marketable securities	49	8
Deferred rent	5
Amortization of lease allowance liability	(10)	(6)
Stock-based compensation	401	140
Research and development services settled with convertible preferred stock		20
Changes in operating assets and liabilities:
Accounts receivable - grant	234	79
Prepaid expenses and other assets	151	(431)
Accounts payable	95	261
Deferred revenue	(20)
Accrued and other liabilities	(87)	475
Net cash used in operating activities	(5,432)	(3,988)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(271)	(2)
Purchases of marketable securities	(32,780)	(2,940)
Proceeds from maturities of marketable securities	7,440	1,750
Net cash used in investing activities	(25,611)	(1,192)
CASH FLOWS FROM FINANCING ACTIVITIES
Payment of deferred offering costs		(98)
Proceeds from employee stock plan purchases and issuance of common stock	96
Net cash provided (used) by financing activities	96	(98)
NET DECREASE IN CASH AND CASH EQUIVALENTS	(30,947)	(5,278)
CASH AND CASH EQUIVALENTS
Beginning of period	47,748	29,294
End of period	16,801	$ 24,016
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Unpaid amounts related to purchase of property and equipment	$ 4