Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
New and Used Vehicle Sales	$ 2,398,189	$ 2,102,297
Vehicle parts sales	85,196	74,665
Used Vehicle Wholesale Sales	104,029	104,157
Maintenance and Repair Sales	264,319	245,033
Parts And Service Sales	349,515	319,698
New Vehicle Retail Sales	1,513,590	1,337,213
Financial Services Revenue	112,322	96,834
Revenues	2,860,026	2,518,829
Used Vehicle Retail Sales	780,570	660,927
UNITED STATES
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
New and Used Vehicle Sales	1,707,785	1,610,741
Vehicle parts sales	74,355	66,754
Used Vehicle Wholesale Sales	54,002	70,545
Maintenance and Repair Sales	210,159	204,405
Parts And Service Sales	284,514	271,159
New Vehicle Retail Sales	1,089,953	1,018,249
Financial Services Revenue	96,187	85,819
Revenues	2,088,486	1,967,719
Used Vehicle Retail Sales	563,830	521,947
UNITED KINGDOM
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
New and Used Vehicle Sales	593,138	404,518
Vehicle parts sales	9,515	6,280
Used Vehicle Wholesale Sales	46,185	30,509
Maintenance and Repair Sales	43,626	30,501
Parts And Service Sales	53,141	36,781
New Vehicle Retail Sales	354,404	258,640
Financial Services Revenue	14,263	9,028
Revenues	660,542	450,327
Used Vehicle Retail Sales	192,549	115,369
BRAZIL
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
New and Used Vehicle Sales	97,266	87,038
Vehicle parts sales	1,326	1,631
Used Vehicle Wholesale Sales	3,842	3,103
Maintenance and Repair Sales	10,534	10,127
Parts And Service Sales	11,860	11,758
New Vehicle Retail Sales	69,233	60,324
Financial Services Revenue	1,872	1,987
Revenues	110,998	100,783
Used Vehicle Retail Sales	$ 24,191	$ 23,611