Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (9,977)	$ (3,895)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	62	35
Amortization of premium on marketable securities	14
Loss on disposal of property and equipment		2
Deferred rent		2
Amortization of lease allowance liability	(12)	(12)
Stock-based compensation	529	184
Research and development services settled with convertible preferred stock	50	540
Changes in operating assets and liabilities:
Accounts receivable-grant	72	(3,427)
Prepaid expenses and other assets	(704)	(230)
Accounts payable	172	444
Accrued and other liabilities	1,174	19
Net cash used in operating activities	(8,620)	(6,338)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(91)	(34)
Purchases of marketable securities	(2,940)
Proceeds from maturities of marketable securities	3,766
Increase in restricted cash	(75)	(10)
Net cash provided by (used in) investing activities	660	(44)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from issuance of convertible preferred stock, net of offering costs		43,684
Proceeds from initial public offering, net of (payments of) offering costs	49,294	(837)
Net cash provided by financing activities	49,294	42,847
NET INCREASE IN CASH	41,334	36,465
CASH
Beginning of period	29,294	2,616
End of period	70,628	39,081
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Deemed dividend to Series A convertible preferred stockholders upon conversion from an LLC to corporation		228
Convertible preferred stock issued for research and development services to be performed		504
Unpaid amounts related to purchase of property and equipment		$ 70
Series A Convertible Preferred Stock
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Conversion of convertible preferred stock to common stock upon initial public offering	13,573
Series B Convertible Preferred Stock
Supplemental Disclosure of Non-Cash Investing and Financing Information:
Conversion of convertible preferred stock to common stock upon initial public offering	$ 44,738