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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
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Accounting Policies [Abstract] |  |
Aggregate Unrealized Losses, Less than one year | $ 1,135,425 gntx_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLossesAccumulatedInAOCI | $ 48,603 gntx_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLossesAccumulatedInAOCI
Continuous unrealized loss position, Aggregate Fair Value | $ 19,972,258 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue | $ 1,886,080 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue

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- Definition Available For Sale Securities Continuous Unrealized Loss Position Less Than 12 Months Aggregate Losses Accumulated In AOCI + References No definition available. + Details
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- Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
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