Borrowings of long term debt related to real estate loans.

No definition available.

Name:	gpi_BorrowingsOfLongTermDebtRelatedToRealEstateLoans
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

+ Details

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Data Type:	num: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

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value amount of debt instrument that was repurchased.

+ References

No definition available.

+ Details

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

- Definition

Face (par) amount of the original debt instrument that was repurchased.

+ References

No definition available.

+ Details

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

- Definition

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

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

- Definition

Amount, after accumulated amortization, of debt premium.

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

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of the cost of borrowed funds accounted for as interest expense for debt.

+ References

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Balance Type:	debit
Period Type:	duration

- 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.

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

- Definition

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

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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+ Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_U.S.NotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_U.K.NotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=gpi_A5.00SeniorNoteMember
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Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Debt - Narrative (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended	12 Months Ended
Debt - Narrative (Details) - USD ($) $ in Millions	Apr. 02, 2020	May 08, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Additional mortgage loans			$ 18.9	$ 0.0
Real estate related
Debt Instrument [Line Items]
Borrowings outstanding			455.9
U.S. Notes
Debt Instrument [Line Items]
Borrowings outstanding			366.0
U.K. Notes
Debt Instrument [Line Items]
Borrowings outstanding			78.9
Brazil Note
Debt Instrument [Line Items]
Borrowings outstanding			$ 11.0
5.00% Senior Notes
Debt Instrument [Line Items]
Interest rate (as a percentage)			5.00%
5.25% Senior Notes
Debt Instrument [Line Items]
Interest rate (as a percentage)			5.25%
Acquisition Line
Debt Instrument [Line Items]
Acquisition line			$ 68.1	$ 72.5
Interest rate (as a percentage)			1.85%
Subsequent Event
Debt Instrument [Line Items]
Premium percentage	102.625%
Unamortized premium	$ 0.6
Loss on redemption	10.4
Write offs of unamortized discount	1.9
Accrued interest	$ 4.6
Additional mortgage loans		$ 130.0
Subsequent Event \| 5.25% Senior Notes
Debt Instrument [Line Items]
Interest rate (as a percentage)	5.25%
Fully redeemed aggregate principal amount	$ 300.0
Principal amount of notes redeemed plus associated premium	$ 307.9