Inventories - Components of Inventories (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Inventory Disclosure [Abstract]
New vehicles	$ 998,390	$ 1,161,490
Used vehicles	322,466	251,103
Service loaners	125,731	121,946
Parts, accessories and other	64,749	65,042
Net inventories	$ 1,511,336	$ 1,599,581