Summary of Quarterly Financial Data (Unaudited) - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended						12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Unaudited Quarterly Financial Data [Line Items]
Pre-tax benefit related to an original equipment manufacturer emissions-related settlement	$ 14,800
Asset impairment charges	1,800	$ 6,100		$ 1,300	$ 10,500	$ 6,200	$ 8,063	$ 17,955	$ 6,594
Pre-tax benefit related to lease exit and storm damage accrual adjustments	400
Pre-tax benefit (charges) related to lease exit accrual adjustments	$ (500)	(1,000)	$ 500
Pre-tax charges against to natural damages		$ 2,300	$ 6,000		4,200
Pre-tax gain (loss) on disposal							$ (47)	$ 2,748	$ 11,079
Pre-tax severance expenses						$ 900
Franchised Dealerships [Member]
Condensed Unaudited Quarterly Financial Data [Line Items]
Pre-tax gain (loss) on disposal				$ 2,300	$ 1,100