Document and Entity Information - $ / shares	9 Months Ended
	Sep. 30, 2015	Oct. 27, 2015	Dec. 31, 2014
Entity Information [Line Items]
Entity Registrant Name	GROUP 1 AUTOMOTIVE INC
Entity Central Index Key	0001031203
Document Type	10-Q
Document Period End Date	Sep. 30, 2015
Amendment Flag	false
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		23,694,561
Common Stock, Par or Stated Value Per Share	$ 0.01		$ 0.01