Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating Activities:
Net loss	$ (6,885)	$ (7,268)
Adjustments to reconcile net loss to net cash provided by / (used in) operating activities:
Depreciation	147	168
Amortization of premium / discount on marketable securities	231	272
Stock-based compensation	1,329	1,383
Changes in operating assets and liabilities:
Interest receivable	(68)	(39)
Accounts receivable	546	(589)
Prepaid expenses and other assets	61	60
Accounts payable and accrued liabilities	(1,480)	(3,070)
Accrued compensation and employee benefits	(1,339)	(676)
Deferred revenues	(560)	12,626
Net cash provided by / (used in) operating activities	(8,018)	2,867
Investing Activities:
Purchases of investments	(16,573)	(12,853)
Maturities of investments	12,910	17,820
Purchases of property and equipment	(68)	(218)
Net cash provided by / (used in) investing activities	(3,731)	4,749
Financing Activities:
Proceeds from issuance of common stock	2,247	108
Net cash provided by financing activities	2,247	108
Net increase / (decrease) in cash and cash equivalents	(9,502)	7,724
Cash and cash equivalents, beginning of period	21,679	16,766
Cash and cash equivalents, end of period	$ 12,177	$ 24,490