Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities
Net loss	$ (18,863)	$ (14,540)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	195	93
Stock-based compensation expense	1,065	655
Accretion of discount/premium on investment securities	77
Noncash interest expense	153	123
Gain on the sale of fixed assets	(25)
Changes in assets and liabilities:
Prepaid expenses and other current assets	(140)	(174)
Accounts payable	210	649
Accrued expenses	(622)	(11)
Deferred rent	(26)	(18)
Net cash used in operating activities	(17,976)	(13,223)
Investing activities
Purchases of available-for-sale securities	(32,111)
Sales and maturities of available-for-sale securities	13,503
Purchases of property and equipment	(388)	(35)
Sale of property and equipment	25
Net cash used in investing activities	(18,971)	(35)
Financing activities
Proceeds from initial public offering, net of issuance costs		62,763
Proceeds from issuance of preferred stock, net of issuance costs		12,331
Proceeds from exercise of common stock options and warrants	111	51
Proceeds from borrowing		5,000
Payments on borrowing	(1,666)
Debt issuance costs		(7)
Net cash (used in) provided by financing activities	(1,555)	80,138
Net (decrease) increase in cash and cash equivalents	(38,502)	66,880
Cash and cash equivalents, beginning of period	62,780	14,668
Cash and cash equivalents, end of period	24,278	81,548
Supplemental disclosure of cash flow information
Cash paid for interest	463	254
Non-cash financing activities
Fixed asset purchases included in accounts payable	$ 21
Warrants for the purchase of series B preferred stock issued in conjunction with credit facility		110
Initial public offering costs in accounts payable and accrued liabilities		970
Reclassification of deferred IPO costs from non-current assets to additional paid-in capital		1,787
Reclassification of warrant liability to additional paid-in capital		$ 206