Equity Plans and Equity Based Compensation (Additional Information) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013 installment
Number of shares available for grant	438,813
Stock granted during period percentage	60.00%	50.00%
Stock cash credit entitlement percentage	40.00%	50.00%
Number of installments			3
Vesting period			2 years
Vested in period percentage			33.30%
Stock issued during period	31,080	29,170
Unrecognized stock expenses in restricted stock	$ 1,873	$ 1,112
Discount from market price, offering date	95.00%
Employee Stock Purchase Plan [Member]
Number of shares available for grant	500,000
Director [Member]
Vested in period percentage	100.00%

Cash credit entitlements as a percent of grant.

No definition available.

Name:	gabc_ScheduleOfShareBasedCompensationRestrictedStockAndRestrictedStockCashCreditEntitlementPercentage
Namespace Prefix:	gabc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Restricted stock as a percent of grant.

+ References

No definition available.

+ Details

Name:	gabc_ScheduleOfShareBasedCompensationRestrictedStockAndRestrictedStockGrantDuringPeriodPercentage
Namespace Prefix:	gabc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Number of Installments

+ References

No definition available.

+ Details

Name:	gabc_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofInstallments
Namespace Prefix:	gabc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The Unrecognized expense associated with the restricted stock grants and cash entitlements.

+ References

No definition available.

+ Details

Name:	gabc_UnrecognizedStockExpensesInRestrictedStock
Namespace Prefix:	gabc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of vesting of share-based compensation awards.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Discount rate from fair value on offering date that participants pay for shares.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares issued during the period related to Restricted Stock Awards, net of any shares forfeited.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration