STATEMENTS OF CASH FLOWS (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Operating Activities:
Net loss	$ (15,659)	$ (29,423)
Reconciliation of net loss to net cash used in operating activities:
Change in fair value of warrant liability	(1,973)	(1,771)
Depreciation and amortization	1,197	991
Amortization of net premiums on short-term investments	317	134
Impairment of property and equipment	60	127
Loss of disposal of property and equipment	0	32
Deferred rent	(254)	(206)
Non-cash stock-based compensation	1,677	1,141
Changes in operating assets and liabilities:
Accounts receivables	37	(341)
Unbilled receivables	(3,848)	0
Prepaid expenses and other current assets	(1,127)	947
Accounts payable and accrued expenses	(3,687)	1,468
Deferred revenue	2,500	(143)
Net cash used in operating activities	(20,760)	(27,044)
Investing Activities:
Capital expenditures	(414)	(1,424)
Proceeds from maturities of short-term investments	20,235	11,000
Purchases of short-term investments	(2,082)	(27,545)
Net cash provided by (used in) by investing activities	17,739	(17,969)
Financing Activities:
Principal payments of notes payable	(60)	(66)
Net proceeds from sales of common stock, net of offering costs of $0.2 million and $0.4 million, respectively	9,182	22,114
Proceeds from the exercise of stock options	156	423
Net cash provided by financing activities	9,278	22,471
Net increase (decrease) in cash and cash equivalents	6,257	(22,542)
Cash and cash equivalents at beginning of period	8,061	38,757
Cash and cash equivalents at end of period	14,318	16,215
Supplemental disclosure of non-cash activities:
Equipment purchases included in accounts payable	168	128
Settlement of notes receivable (See Note 9)	$ 1,522	$ 0