STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities:
Net loss	$ (110,612)	$ (21,380)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	295	339
Stock-based compensation	6,054	3,583
Change in fair value of warrants		(11,529)
Common stock issued in exchange for license agreement	67,285
Loss on disposal of fixed assets	(1)
(Increase) decrease in:
Receivables	(224)	(63)
Prepaid expenses and other current assets	(7,129)	464
Other noncurrent assets		15
Increase (decrease) in:
Accounts payable	2,150	1,531
Accrued expenses	10,956	1,447
Deferred revenue	55,087	(1,033)
Deferred rent	(69)	(154)
Net cash provided by (used in) operating activities	23,792	(26,780)
Cash flows from investing activities:
Purchases of property and equipment	(25)	(193)
Net cash used in investing activities	(25)	(193)
Cash flows from financing activities:
Proceeds from exercise of stock options	3,366	1,323
Repurchase of restricted common stock	(379)	(132)
Repurchase of common stock	(34)
Proceeds from the issuance of common stock, net	94,320
Proceeds from exercise of warrants		3,700
Net cash provided by financing activities	97,273	4,891
Net increase (decrease) in cash and cash equivalents	121,040	(22,082)
Cash and cash equivalents, beginning of period	42,803	68,204
Cash and cash equivalents, end of period	163,843	46,122
Supplementary disclosure of cash flow information:
Cash paid for interest	0	0
Cash paid for income taxes	0	0
Supplementary disclosure of noncash investing and financing activities:
Exercise of equity-classified warrants to common shares		$ 692
Issuance of common stock in license agreement	$ 67,285