XML 14 R48.htm IDEA: XBRL DOCUMENT
v3.3.0.814

Earnings Per Share (Details Textual) - USD ($) $ in Millions | Sep. 30, 2015 | Jun. 25, 2014
--- | --- | ---
2.25% Convertible Notes [Member] |  |
Earnings Per Share (Textual) [Abstract] |  |
Debt Instrument, Interest Rate, Stated Percentage | 2.25% |
2.25% Warrants [Member] |  |
Earnings Per Share (Textual) [Abstract] |  |
Debt Instrument, Interest Rate, Stated Percentage | 2.25% |
3.00% Warrants [Member] |  |
Earnings Per Share (Textual) [Abstract] |  |
Debt Instrument, Interest Rate, Stated Percentage | 3.00% |
3.00% Convertible Notes [Member] |  |
Earnings Per Share (Textual) [Abstract] |  |
Debt Instrument, Interest Rate, Stated Percentage | 3.00% |
Debt Instrument, Repurchased Face Amount |  | $ 92.5
Debt Instrument, Face Amount |  | $ 115.0

X
- Definition Earnings per share. + References No definition available. + Details
Name: | gpi_EarningsPerShareTextualAbstract
Namespace Prefix: | gpi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399 + Details
Name: | us-gaap_DebtInstrumentFaceAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: 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
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Face (par) amount of the original debt instrument that was repurchased. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentRepurchasedFaceAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=gpi_A2.25ConvertibleNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=gpi_A2.25WarrantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_WarrantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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