STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net loss	$ (92,442)	$ (15,287)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	236	217
Stock-based compensation	4,577	2,435
Change in fair value of warrants		(5,682)
Common stock issued in exchange for license agreement	67,285
Loss on disposal of fixed assets	(1)
(Increase) decrease in:
Receivables	55	113
Prepaid expenses and other current assets	(3,302)	957
Other noncurrent assets	(18)	15
Increase (decrease) in:
Accounts payable	1,138	25
Accrued expenses	1,569	1,416
Deferred revenue	(544)	(400)
Deferred rent	19	(98)
Other noncurrent liabilities	17
Net cash used in operating activities	(21,411)	(16,289)
Cash flows from investing activities:
Purchases of property and equipment	(22)	(99)
Net cash used in investing activities	(22)	(99)
Cash flows from financing activities:
Proceeds from exercise of stock options	3,140	1,317
Repurchase of restricted common stock	(246)	(132)
Repurchase of common stock	(34)
Proceeds from the issuance of common stock, net	94,320
Net cash provided by financing activities	97,180	1,185
Net increase (decrease) in cash and cash equivalents	75,747	(15,203)
Cash and cash equivalents, beginning of period	42,803	68,204
Cash and cash equivalents, end of period	118,550	53,001
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		$ 62
Issuance of common stock in license agreement	$ 67,285