XML 31 R81.htm IDEA: XBRL DOCUMENT v2.4.1.9
Income Taxes (Narrative) (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Income Taxes [Abstract]    
Deferred tax valuation allowance $ 3,742,000us-gaap_DeferredTaxAssetsValuationAllowance $ 3,765,000us-gaap_DeferredTaxAssetsValuationAllowance
Deferred tax valuation allowance, state 3,700,000gpre_DeferredTaxAssetsValuationAllowanceState  
Net operating loss carryforwards, federal   $ 30,500,000us-gaap_UnrecognizedTaxBenefitsResultingInNetOperatingLossCarryforward