XML 79 R63.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Summary of Significant Accounting Policies and Estimates - Adoption of Topic 606, "Revenue from Contracts with Customers" (Details) $ in Thousands | Jan. 01, 2018 USD ($)
--- | ---
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Cumulative effect adjustments to retained earnings | $ 11,397
ASU 2014-09 | Adjustment due to Topic 606 | Maintenance and Repair Services |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Cumulative effect adjustments to retained earnings | 4,800
ASU 2014-09 | Adjustment due to Topic 606 | Vehicle Financing, Sale of Service, and Other Insurance Contracts |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Cumulative effect adjustments to retained earnings | $ 6,600

X
- Definition Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption. + References No definition available. + Details
Name: | us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201409Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InitialApplicationPeriodCumulativeEffectTransitionAxis=us-gaap_DifferenceBetweenRevenueGuidanceInEffectBeforeAndAfterTopic606Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=gpi_MaintenanceAndRepairMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=us-gaap_FinancialServiceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |