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Summary of Significant Accounting Policies and Estimates (Details) (USD $)	3 Months Ended					12 Months Ended		3 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Mar. 31, 2014	Jun. 30, 2014	Jun. 25, 2014	Sep. 02, 2014
Summary of Significant Accounting Policies and Estimates [Line Items]
Secured Long-term Debt, Noncurrent	$ 540,100,000us-gaap_SecuredLongTermDebt		$ 0us-gaap_SecuredLongTermDebt			$ 540,100,000us-gaap_SecuredLongTermDebt	$ 0us-gaap_SecuredLongTermDebt
Number of Reportable Segments						3us-gaap_NumberOfReportableSegments
Assets, Current	2,035,219,000us-gaap_AssetsCurrent		1,967,938,000us-gaap_AssetsCurrent			2,035,219,000us-gaap_AssetsCurrent	1,967,938,000us-gaap_AssetsCurrent
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)	25,600,000us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill	5,500,000us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill	5,400,000us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill	7,000,000us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill		31,000,000us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill
Change in the historical chargeback results used in determining estimates of future amounts	10.00%gpi_PercentChangeUsedInSensitivityAnalysis					10.00%gpi_PercentChangeUsedInSensitivityAnalysis
Changed in the reserve of future amounts	2,900,000gpi_SensitivityOfChargeBackInReserve					2,900,000gpi_SensitivityOfChargeBackInReserve
Restricted cash and short term investments	62,100,000gpi_CreditFacilityFloorPlanOffset		56,200,000gpi_CreditFacilityFloorPlanOffset			62,100,000gpi_CreditFacilityFloorPlanOffset	56,200,000gpi_CreditFacilityFloorPlanOffset
Inventory cost reduced for interest assistance received from manufacturers	8,800,000gpi_ManufacturerFloorplanAssistanceRecognizedAsReductionOfInventoryCost		9,000,000gpi_ManufacturerFloorplanAssistanceRecognizedAsReductionOfInventoryCost			8,800,000gpi_ManufacturerFloorplanAssistanceRecognizedAsReductionOfInventoryCost	9,000,000gpi_ManufacturerFloorplanAssistanceRecognizedAsReductionOfInventoryCost
Reduction in new vehicle cost of sales	45,100,000gpi_ManufacturerFloorplanAssistanceRecognizedAsReductionOfCostOfSales		38,500,000gpi_ManufacturerFloorplanAssistanceRecognizedAsReductionOfCostOfSales	33,900,000gpi_ManufacturerFloorplanAssistanceRecognizedAsReductionOfCostOfSales		45,100,000gpi_ManufacturerFloorplanAssistanceRecognizedAsReductionOfCostOfSales	38,500,000gpi_ManufacturerFloorplanAssistanceRecognizedAsReductionOfCostOfSales
Used vehicle days supply						33 days
Weighted Income approach to determine the fair value of the Company's reporting units	80.00%gpi_PercentageWeightedIncomeApproachToDetermineFairValueOfCompanysReportingUnits					80.00%gpi_PercentageWeightedIncomeApproachToDetermineFairValueOfCompanysReportingUnits
Weighted Market approach to determine the fair value of the Company's reporting units	20.00%gpi_PercentageWeightedMarketApproachToDetermineFairValueOfCompanysReportingUnits					20.00%gpi_PercentageWeightedMarketApproachToDetermineFairValueOfCompanysReportingUnits
Recovery back to normalized levels by 2016	17,000,000gpi_ForecastedSeasonallyAdjustedAnnualRateOfNewVehicleSales					17,000,000gpi_ForecastedSeasonallyAdjustedAnnualRateOfNewVehicleSales
Advertising expenses					54,100,000us-gaap_AdvertisingExpense	73,800,000us-gaap_AdvertisingExpense	59,000,000us-gaap_AdvertisingExpense
Reduction in advertising expenses					23,700,000gpi_ManufacturerAdvertisingAssistanceRecognizedAsReductionOfAdvertisingExpense	16,600,000gpi_ManufacturerAdvertisingAssistanceRecognizedAsReductionOfAdvertisingExpense	24,100,000gpi_ManufacturerAdvertisingAssistanceRecognizedAsReductionOfAdvertisingExpense
Percentage of Company's new vehicle sales volume more then which no other manufacturer accounted for						3.00%gpi_PercentageOfCompanysNewVehicleSalesVolumeMoreThenWhichNoOtherManufacturerAccountedFor
Accounts Receivable, Gross, Current	154,971,000us-gaap_AccountsReceivableGrossCurrent		137,463,000us-gaap_AccountsReceivableGrossCurrent			154,971,000us-gaap_AccountsReceivableGrossCurrent	137,463,000us-gaap_AccountsReceivableGrossCurrent
Interest paid					55,800,000us-gaap_InterestPaid	80,200,000us-gaap_InterestPaid	66,200,000us-gaap_InterestPaid
Income taxes refundable					38,600,000us-gaap_ProceedsFromIncomeTaxRefunds	62,300,000us-gaap_ProceedsFromIncomeTaxRefunds	49,000,000us-gaap_ProceedsFromIncomeTaxRefunds
Percentage of change in loss reserve due to change in actuarial loss rate per employee	10.00%gpi_PercentageOfChangeInLossReserveDueToChangeInActuarialLossRatePerEmployee					10.00%gpi_PercentageOfChangeInLossReserveDueToChangeInActuarialLossRatePerEmployee
Change in loss reserve due to change in actuarial loss rate per employee	2,100,000gpi_SensitivityInWorkersCompensationAndGeneralLiabilityReserve					2,100,000gpi_SensitivityInWorkersCompensationAndGeneralLiabilityReserve
Limited exposure in no stop loss plan per occurrence						1,000,000gpi_LimitedExposureInNoStopLossPlanPerOccurrence
Amount Accrued for Stop Loss Plans	500,000gpi_AmountAccruedforStopLossPlans					500,000gpi_AmountAccruedforStopLossPlans
Amount Accrued for No Stop Loss Plans	20,300,000gpi_AmountAccruedforNoStopLossPlans					20,300,000gpi_AmountAccruedforNoStopLossPlans
Maximum potential loss exposure under all of the Stop Loss Plans before consideration of amounts previously paid or accruals recorded	34,900,000gpi_MaximumPotentialLossExposureUnderAllOfStopLossPlansBeforeConsiderationOfAmountsPreviouslyPaidOrAccrualsRecorded					34,900,000gpi_MaximumPotentialLossExposureUnderAllOfStopLossPlansBeforeConsiderationOfAmountsPreviouslyPaidOrAccrualsRecorded
Remaining potential loss exposure in Stop Loss Plan	13,800,000gpi_RemainingPotentialLossExposureInStopLossPlan					13,800,000gpi_RemainingPotentialLossExposureInStopLossPlan
Total assets	4,141,492,000us-gaap_Assets		3,819,478,000us-gaap_Assets			4,141,492,000us-gaap_Assets	3,819,478,000us-gaap_Assets
Liabilities, Current	1,922,199,000us-gaap_LiabilitiesCurrent		1,865,176,000us-gaap_LiabilitiesCurrent			1,922,199,000us-gaap_LiabilitiesCurrent	1,865,176,000us-gaap_LiabilitiesCurrent
Toyota [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume						26.70%gpi_PercentageOfNewVehicleSalesVolume / dei_LegalEntityAxis = gpi_ToyotaMember
Share in company receivable balance	17.70%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_ToyotaMember					17.70%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_ToyotaMember
BMW [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume						11.50%gpi_PercentageOfNewVehicleSalesVolume / dei_LegalEntityAxis = gpi_BmwMember
Share in company receivable balance	14.30%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_BmwMember					14.30%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_BmwMember
Ford [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume						10.90%gpi_PercentageOfNewVehicleSalesVolume / dei_LegalEntityAxis = gpi_FordMember
Share in company receivable balance	8.80%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_FordMember					8.80%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_FordMember
Daimler [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume						4.50%gpi_PercentageOfNewVehicleSalesVolume / dei_LegalEntityAxis = gpi_DaimlerMember
Share in company receivable balance	15.30%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_DaimlerMember					15.30%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_DaimlerMember
General Motors [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume						6.10%gpi_PercentageOfNewVehicleSalesVolume / dei_LegalEntityAxis = gpi_GeneralMotorsMember
Share in company receivable balance	16.00%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_GeneralMotorsMember					16.00%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_GeneralMotorsMember
Nissan [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume						9.40%gpi_PercentageOfNewVehicleSalesVolume / dei_LegalEntityAxis = gpi_NissanMember
Share in company receivable balance	6.70%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_NissanMember					6.70%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_NissanMember
Honda [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume						11.30%gpi_PercentageOfNewVehicleSalesVolume / dei_LegalEntityAxis = gpi_HondaMember
Share in company receivable balance	4.50%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_HondaMember					4.50%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_HondaMember
Chrysler [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume						4.40%gpi_PercentageOfNewVehicleSalesVolume / dei_LegalEntityAxis = gpi_ChryslerMember
Share in company receivable balance	3.20%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_ChryslerMember					3.20%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_ChryslerMember
Hyundai [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume						5.50%gpi_PercentageOfNewVehicleSalesVolume / dei_LegalEntityAxis = gpi_HyundaiMember
Share in company receivable balance	3.80%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_HyundaiMember					3.80%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_HyundaiMember
Volkswagen [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Share in company sales volume						6.40%gpi_PercentageOfNewVehicleSalesVolume / dei_LegalEntityAxis = gpi_VolkswagenMember
Share in company receivable balance	6.50%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_VolkswagenMember					6.50%gpi_PercentageOfAmountsDueFromManufacturers / dei_LegalEntityAxis = gpi_VolkswagenMember
3.00% Convertible Notes due 2020
Summary of Significant Accounting Policies and Estimates [Line Items]
Secured Long-term Debt, Noncurrent	0us-gaap_SecuredLongTermDebt / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroTwoZeroMember		84,305,000us-gaap_SecuredLongTermDebt / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroTwoZeroMember			0us-gaap_SecuredLongTermDebt / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroTwoZeroMember	84,305,000us-gaap_SecuredLongTermDebt / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroTwoZeroMember
Principal amount of Notes										22,600,000us-gaap_DebtInstrumentFaceAmount / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroTwoZeroMember	115,000,000us-gaap_DebtInstrumentFaceAmount / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroTwoZeroMember
2.25% Convertible Notes due 2036
Summary of Significant Accounting Policies and Estimates [Line Items]
Secured Long-term Debt, Noncurrent	0us-gaap_SecuredLongTermDebt / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroThreeSixMember		160,334,000us-gaap_SecuredLongTermDebt / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroThreeSixMember			0us-gaap_SecuredLongTermDebt / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroThreeSixMember	160,334,000us-gaap_SecuredLongTermDebt / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroThreeSixMember
Principal amount of Notes		182,800,000us-gaap_DebtInstrumentFaceAmount / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroThreeSixMember										182,500,000us-gaap_DebtInstrumentFaceAmount / us-gaap_LongtermDebtTypeAxis = gpi_ConvertibleSeniorNotesDueTwoZeroThreeSixMember
Maximum [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Interest assistance received related to vehicles sold								117.70%gpi_InterestAssistanceReceivedRelatedToVehiclesSold / us-gaap_RangeAxis = us-gaap_MaximumMember
Minimum [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Interest assistance received related to vehicles sold									87.30%gpi_InterestAssistanceReceivedRelatedToVehiclesSold / us-gaap_RangeAxis = us-gaap_MinimumMember
UNITED STATES
Summary of Significant Accounting Policies and Estimates [Line Items]
Company operates in different states	14us-gaap_NumberOfStatesInWhichEntityOperates / us-gaap_StatementGeographicalAxis = country_US					14us-gaap_NumberOfStatesInWhichEntityOperates / us-gaap_StatementGeographicalAxis = country_US
Variable Interest Entity, Primary Beneficiary [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Assets, Current	19,049,000us-gaap_AssetsCurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		24,170,000us-gaap_AssetsCurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember			19,049,000us-gaap_AssetsCurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember	24,170,000us-gaap_AssetsCurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Long-Lived Assets	31,783,000us-gaap_NoncurrentAssets / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		71,033,000us-gaap_NoncurrentAssets / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember			31,783,000us-gaap_NoncurrentAssets / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember	71,033,000us-gaap_NoncurrentAssets / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Total assets	50,832,000us-gaap_Assets / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		95,203,000us-gaap_Assets / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember			50,832,000us-gaap_Assets / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember	95,203,000us-gaap_Assets / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Liabilities, Current	16,374,000us-gaap_LiabilitiesCurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		21,653,000us-gaap_LiabilitiesCurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember			16,374,000us-gaap_LiabilitiesCurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember	21,653,000us-gaap_LiabilitiesCurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Liabilities, Noncurrent	15,955,000us-gaap_LiabilitiesNoncurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		25,374,000us-gaap_LiabilitiesNoncurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember			15,955,000us-gaap_LiabilitiesNoncurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember	25,374,000us-gaap_LiabilitiesNoncurrent / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Liabilities	32,329,000us-gaap_Liabilities / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember		47,027,000us-gaap_Liabilities / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember			32,329,000us-gaap_Liabilities / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember	47,027,000us-gaap_Liabilities / us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis = us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
First layer
Summary of Significant Accounting Policies and Estimates [Line Items]
Maximum payout under first layer						0gpi_Maximumpayoutunderfirstlayer / gpi_LayerofcoverageAxis = gpi_FirstlayerMember
First layer | Maximum [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Per Incident Coverage	10,000,000gpi_PerIncidentCoverage / gpi_LayerofcoverageAxis = gpi_FirstlayerMember / us-gaap_RangeAxis = us-gaap_MaximumMember					10,000,000gpi_PerIncidentCoverage / gpi_LayerofcoverageAxis = gpi_FirstlayerMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Aggregate deductible						30,000,000gpi_Aggregatedeductible / gpi_LayerofcoverageAxis = gpi_FirstlayerMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Second layer
Summary of Significant Accounting Policies and Estimates [Line Items]
Hail loss insurance deductibles						20,000,000gpi_Haillossinsurancedeductibles / gpi_LayerofcoverageAxis = gpi_SecondlayerMember
Insurance deductibles for any weather even other than hail						5,000,000gpi_Insurancedeductiblesforanyweatherevenotherthanhail / gpi_LayerofcoverageAxis = gpi_SecondlayerMember
Second layer | Maximum [Member]
Summary of Significant Accounting Policies and Estimates [Line Items]
Aggregate loss coverage	$ 10,000,000gpi_Aggregatelosscoverage / gpi_LayerofcoverageAxis = gpi_SecondlayerMember / us-gaap_RangeAxis = us-gaap_MaximumMember					$ 10,000,000gpi_Aggregatelosscoverage / gpi_LayerofcoverageAxis = gpi_SecondlayerMember / us-gaap_RangeAxis = us-gaap_MaximumMember

X

- Definition

Aggregate deductible

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No definition available.

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- Definition

Aggregate loss coverage

+ References

No definition available.

+ Details

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- Definition

Amount Accrued for No Stop Loss Plans

+ References

No definition available.

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- Definition

Amount Accrued for Stop Loss Plans

+ References

No definition available.

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Balance Type:	credit
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X

- Definition

Credit facility floor plan offset.

+ References

No definition available.

+ Details

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Balance Type:	debit
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- Definition

Forecasted seasonally adjusted annual rate of new vehicle sales.

+ References

No definition available.

+ Details

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X

- Definition

Hail loss insurance deductibles

+ References

No definition available.

+ Details

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Balance Type:	debit
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X

- Definition

Insurance deductibles for any weather even other than hail

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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X

- Definition

Interest assistance received related to vehicles sold.

+ References

No definition available.

+ Details

Name:	gpi_InterestAssistanceReceivedRelatedToVehiclesSold
Namespace Prefix:	gpi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Limited exposure in no stop loss plan per occurrence.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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X

- Definition

Manufacturer advertising assistance recognized as a reduction of advertising expense.

+ References

No definition available.

+ Details

Name:	gpi_ManufacturerAdvertisingAssistanceRecognizedAsReductionOfAdvertisingExpense
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Manufacturer floorplan assistance recognized as reduction of cost of sales.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Manufacturer floorplan assistance recognized as reduction of inventory cost.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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X

- Definition

Maximum payout under first layer

+ References

No definition available.

+ Details

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Balance Type:	debit
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X

- Definition

Maximum potential loss exposure under all of the Stop Loss Plans before consideration of amounts previously paid or accruals recorded.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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X

- Definition

Percentage of amounts due from manufacturers.

+ References

No definition available.

+ Details

Name:	gpi_PercentageOfAmountsDueFromManufacturers
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Data Type:	num:percentItemType
Balance Type:	na
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X

- Definition

Percentage of change in loss reserve due to change in actuarial loss rate per employee.

+ References

No definition available.

+ Details

Name:	gpi_PercentageOfChangeInLossReserveDueToChangeInActuarialLossRatePerEmployee
Namespace Prefix:	gpi_
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Balance Type:	na
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X

- Definition

Percentage of Company's new vehicle sales volume more then which no other manufacturer accounted for.

+ References

No definition available.

+ Details

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- Definition

Percentage of new vehicle sales volume.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
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X

- Definition

Percentage weighted income approach to determine fair value of company's reporting units.

+ References

No definition available.

+ Details

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- Definition

Percentage weighted market approach to determine fair value of company's reporting units.

+ References

No definition available.

+ Details

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X

- Definition

Percent change used in sensitivity analysis.

+ References

No definition available.

+ Details

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X

- Definition

Layer of coverage on the Company's auto physical damage insurance

+ References

No definition available.

+ Details

Name:	gpi_PerIncidentCoverage
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Balance Type:	debit
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- Definition

Remaining Potential Loss Exposure in Stop Loss Plan.

+ References

No definition available.

+ Details

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Balance Type:	credit
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- Definition

Workers compensation and general liability reserve.

+ References

No definition available.

+ Details

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