Condensed Consolidated Statement of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash Flows from Operating Activities
Net loss	$ (42,309)	$ (16,094)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	381	162
Accretion of discounts and amortization of premiums on marketable securities	165
Stock-based compensation	5,232	368
Loss from remeasurement of fair value of warrants	26,077	282
Gain from changes in the fair value of preferred stock derivative liability		(976)
Gain on extinguishment of convertible promissory notes		(3,553)
Non-cash interest expense related to convertible promissory notes payable		2,382
Changes in operating assets and liabilities:
Accounts receivable	6	233
Prepaid expenses and other assets	(2,455)	(468)
Accounts payable	2,209	598
Deferred revenue	165,195	9,693
Accrued clinical trial and manufacturing expenses	1,536	1,015
Accrued expenses and other liabilities	1,717	602
Net cash provided by (used in) operating activities	157,754	(5,756)
Cash Flows from Investing Activities
Purchases of marketable securities	(267,513)
Purchase of property and equipment	(1,816)	(478)
Net cash used in investing activities	(269,329)	(478)
Cash Flows from Financing Activities
Proceeds from issuance of common stock, net of offering costs	150,283
Proceeds from issuance of convertible preferred stock, net of issuance costs	22,522	36,896
Proceeds from issuance of convertible promissory note payable to related parties		308
Proceeds from exercise of stock options and warrants	305	49
Net cash provided by financing activities	173,110	37,253
Net increase in cash and cash equivalents	61,535	31,019
Cash and cash equivalents at beginning of period	119,456	8,532
Cash and cash equivalents at end of period	180,991	39,551
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Conversion of convertible preferred stock to common stock	164,964
Reclassification of warrant liabilities to additional paid-in capital	27,066
Purchase of property and equipment in accounts payable	$ 79	138
Reclassification of liability classified warrants to additional paid-in capital		784
Series C Convertible Preferred Stock
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Issuance of convertible preferred stock in connection with conversion of convertible promissory notes		13,452
Series B Convertible Preferred Stock
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Issuance of convertible preferred stock in connection with conversion of convertible promissory notes		$ 2,088