STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net loss	$ (12,019)	$ (78,231)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	72	122
Stock-based compensation	2,009	1,093
Common stock issued in exchange for license agreement		67,285
Issuance of common stock in a license agreement	87
(Increase) decrease in:
Receivables	(614)	83
Prepaid expenses and other current assets	(3,125)	282
Other noncurrent assets	(5)
Increase (decrease) in:
Accounts payable	(100)	(1,224)
Accrued expenses	(324)	1,037
Deferred revenue	(1,969)	(272)
Deferred rent	(91)	108
Net cash provided by (used in) operating activities	(16,079)	(9,717)
Cash flows from investing activities:
Purchases of property and equipment	(157)	(17)
Net cash used in investing activities	(157)	(17)
Cash flows from financing activities:
Proceeds from exercise of stock options	367	2,541
Repurchase of restricted common stock	(2)	(246)
Proceeds from the issuance of common stock, net		94,320
Net cash provided by financing activities	365	96,615
Net increase (decrease) in cash and cash equivalents	(15,871)	86,881
Cash and cash equivalents, beginning of period	140,717	42,803
Cash and cash equivalents, end of period	124,846	129,684
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