2.4.0.82410403 - Disclosure - Stock-Based Compensation Plans (Details Textual)truefalsefalse1false USDfalsefalse$D2013Q2http://www.sec.gov/CIK0001031203duration2013-04-01T00:00:002013-06-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2false USDfalsefalse$D2012Q2http://www.sec.gov/CIK0001031203duration2012-04-01T00:00:002012-06-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$3false USDfalsefalse$D2013Q2YTDhttp://www.sec.gov/CIK0001031203duration2013-01-01T00:00:002013-06-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$4false USDfalsefalse$D2012Q2YTDhttp://www.sec.gov/CIK0001031203duration2012-01-01T00:00:002012-06-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$1true 2gpi_AdditionalStockBasedCompensationPlansTextualAbstractgpi_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Additional Stock-based Compensation Plans (Textual) [Abstract]2false 3gpi_ProceedsFromOptionExercisesAndEmployeeStockPurchasePlanPurchasesgpi_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse30000003000000USD$falsetruefalse4truefalsefalse31000003100000USD$falsetruefalsexbrli:monetaryItemTypemonetaryThe total cash inflow associated with the amount received from employees to purchase company stock, including stock option exercises.No definition available.false2Cash received from option exercises and employee stock purchase plan purchases3false 3gpi_EmployeeServiceShareBasedCompensationTaxBenefitRealizedFromExerciseOfStockOptionsAndVestingOfRestrictedSharesgpi_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse11000001100000USD$falsefalsefalse4truefalsefalse16000001600000USD$falsefalsefalsexbrli:monetaryItemTypemonetaryEmployee service share based compensation tax benefit realized from exercise of stock options and vesting of restricted shares.No definition available.false2Tax benefit realized for the tax deductions4false 3us-gaap_ShareBasedCompensationus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse36000003600000USD$falsetruefalse2truefalsefalse30000003000000USD$falsetruefalse3truefalsefalse69600006960000USD$falsetruefalse4truefalsefalse59150005915000USD$falsetruefalsexbrli:monetaryItemTypemonetaryThe aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. 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and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 false1Shares available for granted under the incentive plan10false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse6false USDtruefalse$D2013Q2_us-gaap_AwardTypeAxis_gpi_EmployeeStockPurchasePlanMemberhttp://www.sec.gov/CIK0001031203duration2013-04-01T00:00:002013-06-30T00:00:00falsefalseEmployee Stock Purchase Plan [Member]us-gaap_AwardTypeAxisxbrldihttp://xbrl.org/2006/xbrldigpi_EmployeeStockPurchasePlanMemberus-gaap_AwardTypeAxisexplicitMembernumberStandardhttp://www.xbrl.org/2003/instancepurexbrli0sharesStandardhttp://www.xbrl.org/2003/instancesharesxbrli0usdPerShareDividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0USDUSD$nanafalse0Employee Stock Purchase Plan [Member]11true 4gpi_StockBasedCompensationPlansTextualAbstractgpi_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Stock-based Compensation Plans (Textual) [Abstract]12false 5us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedus-gaap_truenainstantfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse35000003500000falsefalsefalse2falsefalsefalse00falsefalsefalse3truefalsefalse35000003500000falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:sharesItemTypesharesThe maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph a -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. 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Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 5 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. 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