XML 26 R24.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Investments (Maturities Of Fixed Income Securities) (Details) (USD $) | Jun. 30, 2012
--- | ---
Investments [Abstract] |
Due within one year | $ 45,947,116
Due between one and five years | 4,239,960
Fixed income securities, total | $ 50,187,076

X
- Definition Fixed income securities, maturities due between one and five years. + References No definition available. + Details
Name: | gntx_FixedIncomeSecuritiesMaturitiesDueBetweenOneAndFiveYears
Namespace Prefix: | gntx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fixed income securities, maturities due within one year. + References No definition available. + Details
Name: | gntx_FixedIncomeSecuritiesMaturitiesDueWithinOneYear
Namespace Prefix: | gntx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fixed income securities total. + References No definition available. + Details
Name: | gntx_FixedIncomeSecuritiesTotal
Namespace Prefix: | gntx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_InvestmentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration