Quarterly report pursuant to Section 13 or 15(d)

Business Acquisitions and Dispositions - Additional Information (Detail)

v3.8.0.1
Business Acquisitions and Dispositions - Additional Information (Detail)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
USD ($)
Franchise
Sep. 30, 2016
Business
Sep. 30, 2016
USD ($)
Business
Franchise
Business Acquisition [Line Items]      
Number of franchises disposed | Franchise     0
Stand-Alone Pre-Owned Vehicle Business [Member]      
Business Acquisition [Line Items]      
Business acquisition, consideration amount $ 76.6    
Stand-Alone Pre-Owned Vehicle Businesses And Related Real Estate [Member]      
Business Acquisition [Line Items]      
Business acquisition, consideration amount     $ 15.9
Number of Business acquired | Business   3 3
Mid-line Import Franchise [Member]      
Business Acquisition [Line Items]      
Number of franchises disposed | Franchise 1    
Net cash generated from disposition $ 22.6