Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Operating activities
Net loss	$ (33,517)	$ (24,679)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	137	247
Gain on disposal of furniture and equipment		(47)
Stock-based compensation expense	6,550	3,479
Amortization of debt issuance costs	329	329
Change in fair value of foreign currency derivative	(732)	(3,168)
Changes in operating assets and liabilities:
Receivables	(1,123)	2,193
Prepaid expenses and other assets	(29)	(559)
Deferred collaboration expense	45	5,120
Accounts payable and accrued expenses	3,602	(4,925)
Interest payable	957	736
Deferred collaboration revenue	(880)	(741)
Net cash used in operating activities	(24,661)	(22,015)
Investing activities
Acquisitions of furniture and equipment	(41)	(26)
Proceeds from sale of furniture and equipment		50
Change in restricted cash	1	158
Purchases of investments	(15,852)	(15,232)
Sales and maturities of investments	29,000	13,845
Net cash provided by (used in) investing activities	13,108	(1,205)
Financing activities
Sale of common stock, net	106,600	23,648
Exercise of stock options	4,636	1,317
Employee stock purchase plan sales	310	124
Receipt of foreign currency derivative collateral		3,290
Net cash provided by financing activities	111,546	28,379
Increase in cash and cash equivalents	99,993	5,159
Cash and cash equivalents at beginning of period	21,164	20,891
Cash and cash equivalents at end of period	$ 121,157	$ 26,050