Deposits - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Deposits Liabilities, Balance Sheet, Reported Amounts [Abstract]
Time deposits of $250 or more and brokered CDs	$ 448,699	$ 353,961
Time deposits originated from outside the geographic area	37,358	4,713
Deposits from principal officers, directors and their affiliates	$ 105,902	$ 64,352

Time Deposits Originated Through Brokers Outside Geographic Area

No definition available.

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

- References

No definition available.

+ Details

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

- Definition

Amount of deposits held by the entity for a related party (entity, shareholder, employee).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480738/235-10-S50-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

+ Details

Name:	us-gaap_RelatedPartyDepositLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of time deposit liabilities, including certificates of deposit, in denominations that meet or exceed the Federal Deposit Insurance Corporation (FDIC) insurance limit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-SubTopic 405
-Topic 942
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478353/942-405-50-1

+ Details

Name:	us-gaap_TimeDepositsAtOrAboveFDICInsuranceLimit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant