Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Operating Activities:
Net loss	$ (12,335)	$ (12,996)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	305	334
Amortization of premium / discount on marketable securities	456	490
Stock-based compensation	2,707	2,607
Changes in operating assets and liabilities:
Interest receivable	(83)	132
Accounts receivable	(789)	(2,322)
Prepaid expenses and other assets	(753)	(268)
Accounts payable and accrued liabilities	(719)	(2,867)
Accrued compensation and employee benefits	(1,030)	(378)
Deferred revenues	(1,070)	12,122
Net cash used in operating activities	(13,311)	(3,146)
Investing Activities:
Purchases of investments	(27,524)	(47,505)
Maturities of investments	27,420	52,120
Purchases of property and equipment	(349)	(263)
Net cash (used in) / provided by investing activities	(453)	4,352
Financing Activities:
Proceeds from issuance of common stock	4,137	504
Net cash provided by financing activities	4,137	504
Net increase / (decrease) in cash and cash equivalents	(9,627)	1,710
Cash and cash equivalents, beginning of period	21,679	16,766
Cash and cash equivalents, end of period	$ 12,052	$ 18,476