Debt Instrument, Restrictive Covenants, Maximum Dividends And Share Repurchases, Amount

No definition available.

Name:	gpi_DebtInstrumentRestrictiveCovenantsMaximumDividendsAndShareRepurchasesAmount
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line of credit facility minimum borrowing capacity for working capital and general corporate purposes, including acquisitions.

+ References

No definition available.

+ Details

Name:	gpi_LineOfCreditFacilityMinimumBorrowingCapacity
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line Of Credit Facility, Sub-limit

+ References

No definition available.

+ Details

Name:	gpi_LineOfCreditFacilitySublimit
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number Of Tranches

+ References

No definition available.

+ Details

Name:	gpi_NumberOfTranches
Namespace Prefix:	gpi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Participating Financial Institution

+ References

No definition available.

+ Details

Name:	gpi_ParticipatingFinancialInstitution
Namespace Prefix:	gpi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt discount (premium).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=124435984&loc=d3e28555-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124435984&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=124435984&loc=d3e28567-108399

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=124435984&loc=d3e28541-108399

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The effective interest rate at the end of the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_A4.00SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_RevolvingCreditFacilityAcquisitionLineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_NewVehiclesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_UsedVehiclesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_FMCCFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_RevolvingCreditFacilityFloorplanLineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_OtherCreditFacilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_RentalVehicleCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_UKCreditFacilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=gpi_A4.00SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

FLOORPLAN NOTES PAYABLE - Narrative (Details)	12 Months Ended
FLOORPLAN NOTES PAYABLE - Narrative (Details)	Dec. 31, 2021 USD ($) tranche institution	Oct. 21, 2021	Dec. 31, 2020 USD ($)
Revolving Credit Facility
Line of Credit Facility
Unamortized discount	$ 2,600,000		$ 3,600,000
Restrictions limit	$ 279,200,000
4.00% Senior Notes
Line of Credit Facility
Interest rate (as a percentage)		4.00%
Acquisition Line
Line of Credit Facility
Interest rate (as a percentage)	1.09%
LIBOR \| New vehicles
Line of Credit Facility
Basis spread on variable rate (as a percentage)	1.10%
LIBOR \| Used vehicles
Line of Credit Facility
Basis spread on variable rate (as a percentage)	1.40%
LIBOR \| Minimum \| Acquisition Line
Line of Credit Facility
Basis spread on variable rate (as a percentage)	1.00%
LIBOR \| Maximum \| Acquisition Line
Line of Credit Facility
Basis spread on variable rate (as a percentage)	2.00%
Prime Rate \| FMCC facility
Line of Credit Facility
Basis spread on variable rate (as a percentage)	1.50%
Line of credit
Line of Credit Facility
Participating financial institutions (institution) \| institution	21
Number of tranches (tranche) \| tranche	2
Outstanding letters of credit	$ 12,600,000		$ 17,800,000
Line of credit \| Revolving Credit Facility
Line of Credit Facility
Maximum borrowing capacity	1,750,000,000
Line of credit \| Floorplan Line
Line of Credit Facility
Maximum borrowing capacity	$ 1,700,000,000
Weighted average interest rate (as a percentage)	1.18%
Commitment fee (as a percentage)	0.15%
Line of credit \| FMCC facility
Line of Credit Facility
Maximum borrowing capacity	$ 300,000,000
Interest rate (as a percentage)	5.50%
Line of credit \| Acquisition Line
Line of Credit Facility
Maximum borrowing capacity	$ 349,000,000
Minimum borrowing capacity	50,000,000
Sub-limit for letters of credit	100,000,000
Line of credit \| Other Credit Facilities
Line of Credit Facility
Outstanding balance	216,500,000
Line of credit \| Rental Vehicles Financed through Credit Facility
Line of Credit Facility
Outstanding balance	91,500,000
Line of credit \| UK Credit Facilities
Line of Credit Facility
Outstanding balance	$ 125,000,000
Line of credit \| Minimum \| Acquisition Line
Line of Credit Facility
Commitment fee (as a percentage)	0.15%
Line of credit \| Minimum \| Rental Vehicles Financed through Credit Facility
Line of Credit Facility
Interest rate (as a percentage)	1.00%
Line of credit \| Minimum \| UK Credit Facilities
Line of Credit Facility
Interest rate (as a percentage)	1.00%
Line of credit \| Maximum \| Acquisition Line
Line of Credit Facility
Commitment fee (as a percentage)	0.40%
Line of credit \| Maximum \| Rental Vehicles Financed through Credit Facility
Line of Credit Facility
Interest rate (as a percentage)	5.00%
Line of credit \| Maximum \| UK Credit Facilities
Line of Credit Facility
Interest rate (as a percentage)	4.00%
Line of credit \| LIBOR \| New vehicles
Line of Credit Facility
Basis spread on variable rate (as a percentage)	1.21%
Line of credit \| LIBOR \| Used vehicles
Line of Credit Facility
Basis spread on variable rate (as a percentage)	1.51%
Line of credit \| LIBOR \| Minimum \| Acquisition Line
Line of Credit Facility
Basis spread on variable rate (as a percentage)	1.00%
Line of credit \| LIBOR \| Maximum \| Acquisition Line
Line of Credit Facility
Basis spread on variable rate (as a percentage)	2.00%
Line of credit \| Prime Rate
Line of Credit Facility
Interest rate (as a percentage)	4.00%
Line of credit \| Prime Rate \| FMCC facility
Line of Credit Facility
Basis spread on variable rate (as a percentage)	1.50%
4.00% Senior Notes \| 4.00% Senior Notes
Line of Credit Facility
Interest rate (as a percentage)	4.00%