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Summary of Significant Accounting and Reporting Policies (Schedule of Unrealized Losses on Investments) (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Accounting Policies [Abstract]    
Aggregate Unrealized Losses, Less than one year $ 1,135,425gntx_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLossesAccumulatedInAOCI $ 48,603gntx_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLossesAccumulatedInAOCI
Continuous unrealized loss position, Aggregate Fair Value $ 19,972,258us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue $ 1,886,080us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue