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Earnings Per Share (Details Textual) | Dec. 31, 2014
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2.25% Purchased Options [Member] |
Earnings Per Share (Textual) [Abstract] |
Debt interest rate | 2.25%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = us-gaap_CallOptionMember
2.25% Notes [Member] |
Earnings Per Share (Textual) [Abstract] |
Debt interest rate | 2.25%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = gpi_TwoPointTwoFivePercentNotesMember
2.25% Warrants [Member] |
Earnings Per Share (Textual) [Abstract] |
Debt interest rate | 2.25%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = gpi_TwoPointTwoFivePercentWarrantsMember
3.00% Notes [Member] |
Earnings Per Share (Textual) [Abstract] |
Debt interest rate | 3.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = gpi_ThreePointZeroZeroPercentNotesMember
3.00% Warrants [Member] |
Earnings Per Share (Textual) [Abstract] |
Debt interest rate | 3.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = us-gaap_WarrantMember
3.00% Purchased Options [Member] |
Earnings Per Share (Textual) [Abstract] |
Debt interest rate | 3.00%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = gpi_ThreePointZeroZeroPercentPurchasedOptionsMember

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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