Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Operating activities
Net loss	$ (27,282)	$ (23,024)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	300	130
Stock-based compensation expense	1,575	1,143
Accretion of discount/premium on investment securities	107
Noncash interest expense	218	209
Gain on the sale of fixed assets	(49)
Changes in assets and liabilities:
Prepaid expenses and other current assets	(147)	(237)
Other assets		2
Accounts payable	178	619
Accrued expenses	252	112
Deferred rent	(26)	(4)
Net cash used in operating activities	(24,874)	(21,050)
Investing activities
Purchases of available-for-sale securities	(41,497)
Sales and maturities of available-for-sale securities	20,584
Purchases of property and equipment	(436)	(60)
Sale of property and equipment	49
Net cash used in investing activities	(21,300)	(60)
Financing activities
Proceeds from initial public offering, net of issuance costs		61,776
Proceeds from issuance of preferred stock, net of issuance costs		12,331
Proceeds from registered direct offering, net of issuance costs	10,730
Proceeds from at-the-market Offering, net of issuance costs	1,483
Proceeds from exercise of common stock options and warrants	145	51
Proceeds from borrowing		5,000
Payments on borrowing	(2,500)
Debt issuance costs		(7)
Net cash provided by financing activities	9,858	79,151
Net (decrease) increase in cash and cash equivalents	(36,316)	58,041
Cash and cash equivalents, beginning of period	62,780	14,668
Cash and cash equivalents, end of period	26,464	72,709
Supplemental disclosure of cash flow information
Cash paid for interest	661	500
Non-cash financing activities
At-the-market offering costs in accounts payable and accrued liabilities	157
Registered direct offering costs in accounts payable and accrued liabilities	$ 123
Warrants for the purchase of series B preferred stock issued in conjunction with credit facility		107
Initial public offering costs in accounts payable and accrued liabilities		32
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