Acquisition line minimum commitment.

No definition available.

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

- Definition

Credit facility.

+ References

No definition available.

+ Details

Name:	gpi_CreditFacilityTextualAbstract
Namespace Prefix:	gpi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument Maturity Date Period

+ References

No definition available.

+ Details

Name:	gpi_DebtInstrumentMaturityDatePeriod
Namespace Prefix:	gpi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

FMCC Offset

+ References

No definition available.

+ Details

Name:	gpi_FMCCOffset
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Floorplan offset.

+ References

No definition available.

+ Details

Name:	gpi_FloorplanOffset
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line of credit facility, maximum borrowing capacity can be extended, amount.

+ References

No definition available.

+ Details

Name:	gpi_LineOfCreditFacilityMaximumBorrowingCapacityCanBeExtendedAmount
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, unamortized cost.

+ References

No definition available.

+ Details

Name:	gpi_LineOfCreditFacilityUnamortizedCost
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Maximum Limit Of Restricted Payment Basket

+ References

No definition available.

+ Details

Name:	gpi_MaximumLimitOfRestrictedPaymentBasket
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Maximum period for outstanding borrowing.

+ References

No definition available.

+ Details

Name:	gpi_MaximumPeriodForOutstandingBorrowing
Namespace Prefix:	gpi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of days related to cancellation of contract.

+ References

No definition available.

+ Details

Name:	gpi_NumberOfDaysRelatedToCancellationOfContract
Namespace Prefix:	gpi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financial institutions.

+ References

No definition available.

+ Details

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

- Definition

Number of Manufacturer-affiliated finance companies.

+ References

No definition available.

+ Details

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

- Definition

Number of tranches

+ References

No definition available.

+ Details

Name:	gpi_Numberoftranches
Namespace Prefix:	gpi_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Restricted Payment Basket

+ References

No definition available.

+ Details

Name:	gpi_RestrictedPaymentBasket
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num: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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

-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=6879938&loc=d3e572229-122910

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

+ Details

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

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ 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 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
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:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
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 available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=gpi_BrazilianCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	gpi_RevolvingCreditFacilityTrancheAxis=gpi_AcquisitionLineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	gpi_AcquisitionLineBorrowingsCurrencyAxis=currency_USD
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	gpi_AcquisitionLineBorrowingsCurrencyAxis=gpi_EurosorPoundSterlingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	gpi_RevolvingCreditFacilityTrancheAxis=gpi_FloorplanLineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	gpi_FloorplanLineInventoryTypeAxis=gpi_NewVehiclesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	gpi_FloorplanLineInventoryTypeAxis=gpi_UsedVehiclesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

Credit Facilities (Details Textual) $ in Thousands	3 Months Ended	6 Months Ended
Credit Facilities (Details Textual) $ in Thousands	Jun. 30, 2015 USD ($) loan	Jun. 30, 2015 USD ($) loan	Dec. 31, 2014 USD ($)
Credit Facility (Textual) [Abstract]
Assets Held-for-sale, Long Lived	$ 23,300	$ 23,300	$ 22,500
Floorplan Offset	$ (22,466)	$ (22,466)	(39,616)
Brazil Credit Facilities [Member] \| Maximum [Member]
Credit Facility (Textual) [Abstract]
Debt interest rate	21.08%	21.08%
Debt Instrument Maturity Date Period	12 months
Brazil Credit Facilities [Member] \| Minimum [Member]
Credit Facility (Textual) [Abstract]
Debt interest rate	16.77%	16.77%
Debt Instrument Maturity Date Period	1 month
FMCC Facility [Member]
Credit Facility (Textual) [Abstract]
Debt Instrument, Basis Spread on Variable Rate		1.50%
Maximum borrowing capacity under line of credit facility	$ 300,000	$ 300,000
Line of Credit Facility, Amount Outstanding	140,900	140,900
Available amount under borrowing capacity	$ 159,100	$ 159,100
Cancellation of agreement	30 days
Debt interest rate	4.75%	4.75%
Revolving Credit Facility [Member]
Credit Facility (Textual) [Abstract]
Maximum borrowing capacity under line of credit facility	$ 1,700,000	$ 1,700,000
Line Of Credit Facility Maximum Borrowing Capacity Can Be Extended Amount	$ 1,950,000	$ 1,950,000
Number of financial institution \| loan	24	24
Number of Manufacturer-affiliated finance companies \| loan	6	6
Expiry date of Revolving Credit Facility	Jun. 20, 2018
Number of tranches	2	2
Acquisition Line Minimum Commitment	$ 100,000	$ 100,000
Line of credit facility, unamortized cost	4,500	4,500
Restricted payment	178,300	178,300
Maximum Limit Of Restricted Payment Basket	125,000	$ 125,000
Revolving Credit Facility [Member] \| Acquisition Line [Member]
Credit Facility (Textual) [Abstract]
Debt Instrument, Basis Spread on Variable Rate		1.50%
Maximum borrowing capacity under line of credit facility	320,000	$ 320,000
Line Of Credit Facility, Minimum Borrowing Capacity	100,000	100,000
Line of Credit Facility, Amount Outstanding	90,721	90,721	$ 69,713
Available amount under borrowing capacity	183,600	183,600
Letters of credit outstanding	$ 45,700	45,700
Revolving Credit Facility [Member] \| Acquisition Line [Member] \| Maximum [Member]
Credit Facility (Textual) [Abstract]
Commitment fees, Percentage	0.45%
Revolving Credit Facility [Member] \| Acquisition Line [Member] \| Minimum [Member]
Credit Facility (Textual) [Abstract]
Commitment fees, Percentage	0.25%
Revolving Credit Facility [Member] \| Acquisition Line [Member] \| United States of America, Dollars
Credit Facility (Textual) [Abstract]
Line of Credit Facility, Amount Outstanding	$ 90,700	$ 90,700
Revolving Credit Facility [Member] \| Acquisition Line [Member] \| United States of America, Dollars \| Maximum [Member]
Credit Facility (Textual) [Abstract]
Debt Instrument, Basis Spread on Variable Rate		1.00%
Revolving Credit Facility [Member] \| Acquisition Line [Member] \| United States of America, Dollars \| Minimum [Member]
Credit Facility (Textual) [Abstract]
Debt Instrument, Basis Spread on Variable Rate		0.00%
Revolving Credit Facility [Member] \| Acquisition Line [Member] \| Euros or Pound Sterling [Member] \| Maximum [Member]
Credit Facility (Textual) [Abstract]
Debt Instrument, Basis Spread on Variable Rate		2.50%
Maximum borrowing capacity under line of credit facility	$ 125,000	$ 125,000
Revolving Credit Facility [Member] \| Acquisition Line [Member] \| Euros or Pound Sterling [Member] \| Minimum [Member]
Credit Facility (Textual) [Abstract]
Debt Instrument, Basis Spread on Variable Rate		1.50%
Revolving Credit Facility [Member] \| Floorplan Line [Member]
Credit Facility (Textual) [Abstract]
Commitment fees, Percentage	0.20%
Line of Credit Facility, Amount Outstanding	$ 1,181,900	$ 1,181,900
Available amount under borrowing capacity	198,100	198,100
Floorplan Offset	$ (22,500)	$ (22,500)
Weighted average interest rate	1.40%	1.40%	1.40%
Maximum period for outstanding borrowing	1 year
Revolving Credit Facility [Member] \| Floorplan Line [Member] \| Maximum [Member]
Credit Facility (Textual) [Abstract]
Maximum borrowing capacity under line of credit facility	$ 1,600,000	$ 1,600,000
Revolving Credit Facility [Member] \| Floorplan Line [Member] \| New Vehicle [Member]
Credit Facility (Textual) [Abstract]
Debt Instrument, Basis Spread on Variable Rate		1.25%
Revolving Credit Facility [Member] \| Floorplan Line [Member] \| Used Vehicles [Member]
Credit Facility (Textual) [Abstract]
Debt Instrument, Basis Spread on Variable Rate		1.50%
Rental Vehicle Credit Facility [Member]
Credit Facility (Textual) [Abstract]
Debt interest rate	4.75%	4.75%
UK Credit Facilities [Member] \| Maximum [Member]
Credit Facility (Textual) [Abstract]
Debt interest rate	3.95%	3.95%
UK Credit Facilities [Member] \| Minimum [Member]
Credit Facility (Textual) [Abstract]
Debt interest rate	1.15%	1.15%