STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:
Net loss	$ (21,380)	$ (48,203)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	339	582
Stock-based compensation	3,583	2,482
Change in fair value of warrants	(11,529)	(2,979)
Loss on disposal of fixed assets		194
Common stock issued in exchange for in-process research and development	0	0
(Increase) decrease in:
Receivables	(63)	(391)
Prepaid expenses and other current assets	464	3,717
Other noncurrent assets	15	262
Deposits		5
Increase (decrease) in:
Accounts payable	1,531	(618)
Accrued expenses	1,447	(4,943)
Deferred revenue	(1,033)	(600)
Deferred rent	(154)	8
Other noncurrent liabilities		20
Net cash used in operating activities	(26,780)	(50,464)
Cash flows from investing activities:
Purchases of property and equipment	(193)	(119)
Proceeds from sale of property and equipment		1
Net cash used in investing activities	(193)	(118)
Cash flows from financing activities:
Proceeds from exercise of stock options	1,323	956
Payments to employees for repurchase of common stock	(132)	(250)
Proceeds from exercise of warrants	3,700	201
Net cash provided by financing activities	4,891	907
Net increase (decrease) in cash and cash equivalents	(22,082)	(49,675)
Cash and cash equivalents, beginning of period	68,204	73,306
Cash and cash equivalents, end of period	46,122	23,631
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	$ 142