Loans - Schedule of Loans Acquired (Details) - Bank Acquisition - USD ($) $ in Thousands	Mar. 31, 2022	Jan. 01, 2022
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Acquired Loan Balance	$ 659,212	$ 683,526
Fair Value Discounts		(5,359)
Fair Value		$ 678,167
Fair Value Discount, remaining carrying amount	$ 4,628

Business Combination, Acquired Receivables, Fair Value Discounts

No definition available.

Name:	gabc_BusinessCombinationAcquiredReceivablesFairValueDiscounts
Namespace Prefix:	gabc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of acquired receivable from business combination, excluding certain loans and debt securities acquired in transfer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=123413009&loc=d3e4845-128472

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the gross contractual amounts receivable, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=123413009&loc=d3e4845-128472

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unamortized purchase premium (discount) on financing receivable. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5074-111524

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_BusinessAcquisitionAxis=gabc_CitizensUnionBancorpOfShelbyvilleIncCUBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: