STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net loss	$ (24,850)	$ (10,833)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	11	5
Stock-based compensation expense	2,108	698
Change in fair value of warrant liability		(1,192)
Amortization of debt issuance costs	7	4
Loss on disposal of fixed assets	2
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(947)	1,344
Accounts payable and accrued expenses	3,540	1,385
Net cash used in operating activities	(20,129)	(8,589)
Cash flows from investing activities
Purchases of investments	(7,705)	(33)
Maturities of short-term investments	1,743
Deposit on equipment	(352)
Net cash used in investing activities	(6,314)	(33)
Cash flows from financing activities
Proceeds from exercise of stock options	373	128
Repayment of notes payable	(206)
Proceeds from initial public offering, net of offering costs	28,278	41,202
Proceeds from notes payable, net of issuance costs		6,975
Net cash provided by financing activities	28,445	48,305
Net increase in cash and cash equivalents	2,002	39,683
Cash and cash equivalents-beginning of period	49,720	10,037
Cash and cash equivalents-end of period	51,722	49,720
Supplemental disclosure of cash flow information
Conversion of preferred stock to common stock		70,340
Cash paid for interest	468	89
Financing arrangement with third-party vendor	584
Issuance of Series C Preferred Stock		$ 500
Accrued public offering costs	$ 142