STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities
Net loss	$ (17,237)	$ (7,226)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	8	7
Stock-based compensation expense	1,368	263
Change in fair value of warrant liability		(1,192)
Amortization of debt issuance costs	5	3
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,260)	1,332
Accounts payable and accrued expenses	2,036	192
Net cash used in operating activities	(15,080)	(6,621)
Cash flows from investing activities
Purchases of investments	(6,961)
Maturities of short-term investments	498
Deposit on equipment	(352)
Net cash used in investing activities	(6,815)
Cash flows from financing activities
Proceeds from exercise of stock options	373	28
Repayment of notes payable	(82)
Proceeds from initial public offering, net of offering costs		41,672
Proceeds from notes payable, net of issuance costs		1,989
Payment of deferred offering costs	(89)
Net cash provided by financing activities	202	43,689
Net (decrease)/increase in cash and cash equivalents	(21,693)	37,068
Cash and cash equivalents-beginning of period	49,720	10,037
Cash and cash equivalents-end of period	28,027	47,105
Supplemental disclosure of cash flow information
Conversion of preferred stock to common stock		70,340
Cash paid for interest	348	46
Financing arrangement with third-party vendor	$ 584
Issuance of Series C Preferred Stock		500
Accrued initial public offering costs		$ 469