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v3.10.0.1

Commitments and Off-balance Sheet Items (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2018
Minimum |
Commitments and Contingent Liabilities [Line Items] |
Loans and Leases Receivable Fixed Commitment Interest Rates | 2.00%
Loans and Leases Receivable Fixed Commitment Maturity | 1 year
Maximum |
Commitments and Contingent Liabilities [Line Items] |
Loans and Leases Receivable Fixed Commitment Interest Rates | 21.00%
Loans and Leases Receivable Fixed Commitment Maturity | 32 years

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- References No definition available. + Details
Name: | gabc_CommitmentsAndContingentLiabilitiesLineItems
Namespace Prefix: | gabc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage of loans and leases receivable fixed commitment interest rates during the period. + References No definition available. + Details
Name: | gabc_LoansAndLeasesReceivableFixedCommitmentInterestRates
Namespace Prefix: | gabc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Fixed rate commitments to fund loans maturity period. + References No definition available. + Details
Name: | gabc_LoansAndLeasesReceivableFixedCommitmentMaturity
Namespace Prefix: | gabc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |