Condensed Consolidating Financial Information - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ 263,106	$ 52,162
Cash paid in acquisitions, net of cash received	(74,865)	(95)
Proceeds from disposition of franchises, property and equipment	75,923	2,582
Purchases of property and equipment, including real estate	(88,230)	(67,266)
Deposits for real estate and dealership acquisitions	(655)	(57,099)
Other	0	2,074
Net cash used in investing activities	(87,827)	(119,804)
Borrowings on credit facility - floorplan line and other	3,323,798	3,369,580
Repayments on credit facility - floorplan line and other	(3,461,494)	(3,288,367)
Borrowings on credit facility - acquisition line	98,596	47,509
Repayments on credit facility - acquisition line	(84,884)	(15,000)
Borrowings on other debt	111,142	5,137
Principal payments on other debt	(75,784)	(542)
Borrowings on debt related to real estate, net of debt issue costs	54,711	12,901
Principal payments on debt related to real estate	(63,368)	(13,897)
Employee stock purchase plan purchases, net of employee tax withholdings	11	2,487
Repurchases of common stock, amounts based on settlement date	(51,276)	(39,025)
Proceeds from termination of mortgage swap	918	0
Dividends paid	(10,836)	(10,200)
Borrowings (repayments) with subsidiaries	0	0
Investment in subsidiaries	0	0
Net cash provided by (used in) financing activities	(158,466)	70,583
EFFECT OF EXCHANGE RATE CHANGES ON CASH	(2,812)	117
NET INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	14,001	3,058
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH, beginning of period	29,631	24,246
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH, end of period	43,632	27,304
Group 1 Automotive, Inc.
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	92,277	73,072
Cash paid in acquisitions, net of cash received	0	0
Proceeds from disposition of franchises, property and equipment	0	0
Purchases of property and equipment, including real estate	0	0
Deposits for real estate and dealership acquisitions	(400)	0
Other	0	0
Net cash used in investing activities	(400)	0
Borrowings on credit facility - floorplan line and other	0	0
Repayments on credit facility - floorplan line and other	0	0
Borrowings on credit facility - acquisition line	98,596	47,509
Repayments on credit facility - acquisition line	(84,884)	(15,000)
Borrowings on other debt	0	0
Principal payments on other debt	(24,741)	0
Borrowings on debt related to real estate, net of debt issue costs	0	0
Principal payments on debt related to real estate	0	0
Employee stock purchase plan purchases, net of employee tax withholdings	11	2,487
Repurchases of common stock, amounts based on settlement date	(51,276)	(39,025)
Proceeds from termination of mortgage swap	0
Dividends paid	(10,836)	(10,200)
Borrowings (repayments) with subsidiaries	(35,703)	32,214
Investment in subsidiaries	16,956	(91,057)
Net cash provided by (used in) financing activities	(91,877)	(73,072)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0	0
NET INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	0	0
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH, beginning of period	0	0
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH, end of period	0	0
Guarantor Subsidiaries
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	155,215	(32,554)
Cash paid in acquisitions, net of cash received	(31,144)	0
Proceeds from disposition of franchises, property and equipment	73,785	265
Purchases of property and equipment, including real estate	(56,116)	(60,594)
Deposits for real estate and dealership acquisitions	(255)	273
Other	0	2,074
Net cash used in investing activities	(13,730)	(57,982)
Borrowings on credit facility - floorplan line and other	3,261,353	3,319,971
Repayments on credit facility - floorplan line and other	(3,412,939)	(3,244,979)
Borrowings on credit facility - acquisition line	0	0
Repayments on credit facility - acquisition line	0	0
Borrowings on other debt	60,081	0
Principal payments on other debt	(24,209)	(542)
Borrowings on debt related to real estate, net of debt issue costs	42,656	0
Principal payments on debt related to real estate	(54,144)	(11,183)
Employee stock purchase plan purchases, net of employee tax withholdings	0	0
Repurchases of common stock, amounts based on settlement date	0	0
Proceeds from termination of mortgage swap	918
Dividends paid	0	0
Borrowings (repayments) with subsidiaries	18,141	(65,909)
Investment in subsidiaries	(34,762)	91,017
Net cash provided by (used in) financing activities	(142,905)	88,375
EFFECT OF EXCHANGE RATE CHANGES ON CASH	0	0
NET INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(1,420)	(2,161)
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH, beginning of period	10,096	8,039
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH, end of period	8,676	5,878
Non-Guarantor Subsidiaries
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	15,614	11,644
Cash paid in acquisitions, net of cash received	(43,721)	(95)
Proceeds from disposition of franchises, property and equipment	2,138	2,317
Purchases of property and equipment, including real estate	(32,114)	(6,672)
Deposits for real estate and dealership acquisitions	0	(57,372)
Other	0	0
Net cash used in investing activities	(73,697)	(61,822)
Borrowings on credit facility - floorplan line and other	62,445	49,609
Repayments on credit facility - floorplan line and other	(48,555)	(43,388)
Borrowings on credit facility - acquisition line	0	0
Repayments on credit facility - acquisition line	0	0
Borrowings on other debt	51,061	5,137
Principal payments on other debt	(26,834)	0
Borrowings on debt related to real estate, net of debt issue costs	12,055	12,901
Principal payments on debt related to real estate	(9,224)	(2,714)
Employee stock purchase plan purchases, net of employee tax withholdings	0	0
Repurchases of common stock, amounts based on settlement date	0	0
Proceeds from termination of mortgage swap	0
Dividends paid	0	0
Borrowings (repayments) with subsidiaries	17,562	33,695
Investment in subsidiaries	17,806	40
Net cash provided by (used in) financing activities	76,316	55,280
EFFECT OF EXCHANGE RATE CHANGES ON CASH	(2,812)	117
NET INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	15,421	5,219
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH, beginning of period	19,535	16,207
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH, end of period	$ 34,956	$ 21,426