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v2.4.1.9

Consolidated Statement of Stockholders' Equity (Parenthetical) | 3 Months Ended
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Mar. 31, 2015
3.00% Convertible Notes [Member] |
Convertible senior notes stated rate |
2.25% Convertible Notes [Member] |
Convertible senior notes stated rate |

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- Definition Equity component convertible note rate. + References No definition available. + Details
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Namespace Prefix: | gpi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_LongtermDebtTypeAxis=gpi_A3.00ConvertibleNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |