Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Operating activities
Net loss	$ (24,786)	$ (16,678)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	97	183
Stock-based compensation expense	5,129	2,521
Amortization of debt issuance costs	220	220
Change in fair value of foreign currency derivative	3,350	(3,071)
Changes in operating assets and liabilities:
Receivables	1,218	3,538
Prepaid expenses and other assets	(408)	(53)
Deferred collaboration expense	30	5,106
Accounts payable and accrued expenses	(247)	(7,072)
Interest payable	(81)	1,660
Deferred collaboration revenue	(583)	(447)
Net cash used in operating activities	(16,061)	(14,093)
Investing activities
Acquisitions of furniture and equipment	(7)	(26)
Change in restricted cash	1	(1,821)
Purchases of investments	(12,651)	(369)
Sales and maturities of investments	20,900	6,820
Net cash provided by investing activities	8,243	4,604
Financing activities
Sale of common stock, net	106,600	5,171
Exercise of stock options	4,145	346
Employee stock purchase plan sales	128	68
(Payment) receipt of foreign currency derivative collateral	(2,700)	2,780
Net cash provided by financing activities	108,173	8,365
Increase (decrease) in cash and cash equivalents	100,355	(1,124)
Cash and cash equivalents at beginning of period	21,164	20,891
Cash and cash equivalents at end of period	$ 121,519	$ 19,767