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Reconciliation Between Effective Tax Rate and Income Tax Rate (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Schedule Of Effective Tax Rates Line Items      
Federal income tax rate 34.00% 34.00% 34.00%
Research and development tax credits (0.60%) 54.60% 3.90%
Valuation allowance (7.50%) (507.40%) (16.80%)
Permanent Differences (25.90%) 450.00% (12.80%)
Other 0.00% (31.20%) (8.30%)
Effective tax rate 0.00% 0.00% 0.00%