STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net loss	$ (143,219)	$ (92,442)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	155	236
Stock-based compensation	4,075	4,577
Common stock issued in exchange for license agreement		67,285
Preferred stock obligation in exchange for license agreement	119,045
Issuance of common stock in a license agreement	87
Loss on disposal of fixed assets		(1)
(Increase) decrease in:
Receivables	431	55
Prepaid expenses and other current assets	(6,332)	(3,302)
Other noncurrent assets	1	(18)
Increase (decrease) in:
Accounts payable	23	1,138
Accrued expenses	(1,513)	1,569
Deferred revenue	(3,666)	(544)
Deferred rent	(239)	19
Other noncurrent liabilities		17
Net cash used in operating activities	(31,152)	(21,411)
Cash flows from investing activities:
Purchases of property and equipment	(257)	(22)
Net cash used in investing activities	(257)	(22)
Cash flows from financing activities:
Proceeds from exercise of stock options	551	3,140
Repurchase of restricted common stock	(853)	(246)
Repurchase of common stock	(2)	(34)
Proceeds from issuance of common stock, net		94,320
Net cash provided by financing activities	(304)	97,180
Net increase (decrease) in cash and cash equivalents	(31,713)	75,747
Cash and cash equivalents, beginning of period	140,717	42,803
Cash and cash equivalents, end of period	109,004	118,550
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:
Issuance of common stock in license agreement		$ 67,285
Series 1 preferred stock issuance obligation issued in a license agreement	$ 119,045