Fair Value of Financial Instruments - Estimated Incremental Borrowing Rates for Similar Types of Borrowing Arrangements (Parenthetical) (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Level 3 [Member] | Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Manufacturer flooring plans payable, interest rate	3.50%	3.50%
Level 3 [Member] | Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Manufacturer flooring plans payable, interest rate	3.50%	3.50%
Level 2 [Member] | Carrying Amount [Member] | Senior Unsecured Notes Due 2028 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior unsecured notes, interest rate	3.875%	3.875%
Senior unsecured notes, due year	2028	2028
Level 2 [Member] | Fair Value [Member] | Senior Unsecured Notes Due 2028 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Senior unsecured notes, interest rate	3.875%	3.875%
Senior unsecured notes, due year	2028	2028