Inventories - Components of Inventories (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
New vehicles	$ 1,116,708	$ 1,088,814
Used vehicles	301,283	282,288
Service loaners	133,552	128,821
Parts, accessories and other	70,795	70,778
Net inventories	$ 1,622,338	$ 1,570,701