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Intangible Franchise Rights and Goodwill (Details Textual) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Countries and States [Line Items]      
Accumulated Impairments 42.4gpi_AccumulatedImpairments    
Intangible Franchise Rights and Goodwill (Textual) [Abstract]      
Number Of Dealerships Acquired     16gpi_NumberOfDealershipsAcquired
UNITED STATES      
Intangible Franchise Rights and Goodwill (Textual) [Abstract]      
Number Of Dealerships Acquired 7gpi_NumberOfDealershipsAcquired
/ gpi_CountriesAndStatesAxis
= country_US		 9gpi_NumberOfDealershipsAcquired
/ gpi_CountriesAndStatesAxis
= country_US		 10gpi_NumberOfDealershipsAcquired
/ gpi_CountriesAndStatesAxis
= country_US
BRAZIL      
Intangible Franchise Rights and Goodwill (Textual) [Abstract]      
Number Of Dealerships Acquired 1gpi_NumberOfDealershipsAcquired
/ gpi_CountriesAndStatesAxis
= country_BR		 18gpi_NumberOfDealershipsAcquired
/ gpi_CountriesAndStatesAxis
= country_BR		  
UNITED KINGDOM      
Intangible Franchise Rights and Goodwill (Textual) [Abstract]      
Number Of Dealerships Acquired 3gpi_NumberOfDealershipsAcquired
/ gpi_CountriesAndStatesAxis
= country_GB		 4gpi_NumberOfDealershipsAcquired
/ gpi_CountriesAndStatesAxis
= country_GB		 6gpi_NumberOfDealershipsAcquired
/ gpi_CountriesAndStatesAxis
= country_GB