| **SOI Limited partnerships Sec Lending Special Deposits (Details 5) (USD $)In Thousands, unless otherwise specified** | 12 Months Ended                                                                                         |                                                                               |
|-----------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------|
||
| **Investments, Debt and Equity Securities [Abstract]**                                                                |                                                                                                    |                                                                          |
| Limited partnership and other corporation interests                                                                   | $ 49,421us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures                           | $ 79,236us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures |
| Interest in various upper-tier LIHLPs (as a percent)                                                                  | 99.00%us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPMembersOrLimitedPartnersOwnershipInterest |                                                                          |
| **Nature and activities of the VIEs and the effect on financial statements**                                          |                                                                                                    |                                                                          |
| Carrying value in relation to the activities of the VIEs                                                              | 7,464us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets                                     | 31,563us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets          |
| Maximum exposure to loss in relation to the activities of the VIEs                                                    | 7,464us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount                                      | 31,563us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount           |
| **Special deposits and securities lending**                                                                           |                                                                                                    |                                                                          |
| Fair value of securities on deposit with governmental authorities                                                     | 14,612us-gaap_CashAndSecuritiesSegregatedUnderFederalAndOtherRegulations                                | 14,072us-gaap_CashAndSecuritiesSegregatedUnderFederalAndOtherRegulations      |
| Securities loaned to third parties at amortized cost                                                                  | 15,252us-gaap_SecuritiesLoaned                                                                          | 28,178us-gaap_SecuritiesLoaned                                                |
| Estimated fair value of securities loaned to third parties                                                            | 15,423gac_SecuritiesLoanedFairValue                                                                     | 27,166gac_SecuritiesLoanedFairValue                                           |
| Restricted cash received as collateral                                                                                | 13,741us-gaap_DepositsReceivedForSecuritiesLoanedAtCarryingValue                                        | 18,534us-gaap_DepositsReceivedForSecuritiesLoanedAtCarryingValue              |
| Securities received as collateral                                                                                     | $ 2,131gac_SecuritiesReceivedForSecuritiesLoanedAtCarryingValue                                         | $ 9,424gac_SecuritiesReceivedForSecuritiesLoanedAtCarryingValue               |

| X                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value of securities loaned to other entities.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of securities received as collateral in return for loaning securities to another party.
+ References
No definition available.
+ Details**Name:**gac_SecuritiesReceivedForSecuritiesLoanedAtCarryingValue**Namespace Prefix:**gac_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of cash subject to withdrawal restrictions, restricted deposits held as compensating balances, and cash and securities segregated in compliance with regulations (such as cash deposited in a special reserve account for the exclusive benefit of customers).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 305 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6478312&loc=d3e61473-112792
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| X                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DepositAssetsDisclosureAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of cash received as security in return for loaning securities to another party.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.12) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878
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| X                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Total investments in (A) an entity in which the entity has significant influence, but does not have control, (B) subsidiaries that are not required to be consolidated and are accounted for using the equity and or cost method, and (C) an entity in which the reporting entity shares control of the entity with another party or group. Includes long-term advances receivable from a party that is affiliated with the reporting entity by means of direct or indirect ownership.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of units or percentage investment held by one or more members or limited partners of the LLC or LP.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 272 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after the effects of master netting arrangements, of securities loaned to entities in exchange for collateral. Includes liabilities not subject to a master netting arrangement.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=20225523&loc=SL20225862-175312Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226008-175313Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 50 -Paragraph 1A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7523297&loc=SL6224234-111729Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 405 -Section 55 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6476329&loc=d3e44140-110984
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5710-111685
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| X                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).
+ References
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