Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities:
Net loss	$ (45,189)	$ (30,108)	$ (39,081)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization, and impairment	177	304	628
Loss (gain) on disposal of furniture and equipment	27	(47)
Stock-based compensation expense	10,177	4,368	4,167
Amortization of debt issuance costs	439	439	439
Change in fair value of foreign currency derivative	(5,487)	(5,294)	749
Changes in operating assets and liabilities:
Receivables	(7,375)	2,447	1,269
Inventory	(683)		263
Prepaid expenses and other assets	(1,943)	(620)	(623)
Deferred collaboration expense	59	5,133	2,301
Accounts payable and accrued expenses	6,818	(2,049)	2,068
Deferred revenue	4,429	(1,103)	(9,577)
Net cash used in operating activities:	(38,551)	(26,530)	(37,397)
Investing activities:
Acquisition of furniture and equipment	(106)	(30)	(113)
Proceeds from sale of furniture and equipment		50
Change in restricted cash	1	157	317
Purchases of investments	(73,875)	(23,974)	(16,153)
Sales and maturities of investments	34,000	20,330	40,833
Net cash (used in) provided by investing activities:	(39,980)	(3,467)	24,884
Financing activities:
Sale of common stock, net	106,600	23,633	17,805
Exercise of stock options	4,997	1,333	534
Employee stock purchase plan sales	310	124	321
Receipt (payment) of foreign currency derivative collateral		5,180	(1,700)
Net cash provided by financing activities:	111,907	30,270	16,960
Increase in cash and cash equivalents	33,376	273	4,447
Cash and cash equivalents at beginning of year	21,164	20,891	16,444
Cash and cash equivalents at end of year	$ 54,540	$ 21,164	$ 20,891