STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating Activities:
Net loss	$ (19,364)	$ (35,708)	$ (40,346)
Reconciliation of net loss to net cash used in operating activities:
Change in fair value of warrant liability	(2,474)	(1,671)	1,972
Depreciation and amortization	1,613	1,372	1,194
Amortization of deferred financing costs			147
Amortization of debt discount			222
Loss on disposal of property and equipment		35	21
Impairment of long-lived assets	360	162	23
Amortization of net premiums on short-term investments	317	247
Deferred rent	(341)	(282)	(279)
Non-cash stock-based compensation	2,047	1,339	1,533
Net impairment of short-term investments			490
Changes in operating assets and liabilities:
Accounts receivables	(1,911)	204	32
Unbilled receivables	(1,836)
Prepaid expenses and other assets	(1,854)	(312)	(536)
Accounts payable and accrued expenses	(2,686)	1,912	2,547
Deferred revenue	2,500	(150)	150
Net cash used in operating activities	(23,629)	(32,852)	(32,830)
Investing Activities:
Capital expenditures	(610)	(1,556)	(745)
Purchases of short-term investments	(2,082)	(38,717)
Proceeds from maturities of short-term investments	21,235	19,000	3,100
Net cash provided by (used in) by investing activities	18,543	(21,273)	2,355
Financing Activities:
Principal payments of notes payable	(80)	(86)	(15,043)
Proceeds from settlement of notes receivable from former directors	50
Net proceeds from sales of common stock, net of offering costs of $0.2 million, $0.5 million and $2.7 million, respectively	10,980	23,089	56,385
Proceeds from the exercise of stock options	179	426	952
Net cash provided by financing activities	11,129	23,429	42,294
Net increase (decrease) in cash and cash equivalents	6,043	(30,696)	11,819
Cash and cash equivalents at beginning of year	8,061	38,757	26,938
Cash and cash equivalents at end of year	14,104	8,061	38,757
Supplemental disclosure of non-cash activities:
Conversion of convertible debt and accrued interest to common stock			7,660
Equipment purchases included in accounts payable and accrued expenses	14	418	66
Settlement of notes receivable from former directors	1,522
Sale of common stock under the At Market Issuance Sales Agreement not settled at year-end	847
Supplemental disclosure of cash flow information:
Cash interest payments			$ 817