Financing - Additional Information (Detail) (USD $)	12 Months Ended								1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Aug. 31, 2011	Dec. 31, 2013 Maximum	Dec. 31, 2013 Line of Credit	Dec. 31, 2013 Master Notes	Dec. 31, 2012 Master Notes	Nov. 30, 2009 Master Notes Interest Rate Lock Commitments	Dec. 31, 2010 Master Notes Senior Unsecured Notes, 3.81 Percent, Due May 2018	Dec. 31, 2010 Master Notes Senior Unsecured Notes, 4.60 Percent, Due May 2021	Dec. 31, 2013 Master Notes Senior Unsecured Notes Three Point One Three Percent Due December Twenty Twenty [Member]
Line of Credit Facility [Line Items]
Gain on interest rate lock settlement									$ 251,000
Deferred tax related to interest rate lock settlement	(5,892,000)	(28,901,000)	(16,946,000)						149,000
Letter of credit outstanding	19,102,000
Debt outstanding from dealers	1,163,545,000
Revolving loan facility, maximum capacity				350,000,000
Long-term Line of Credit						80,500,000
Issuance of senior notes										25,000,000	75,000,000	100,000,000
Interest rate for purchase agreement										3.81%	4.60%	3.13%
Maturity date										5/31/2018	5/31/2021	12/31/2020
Long-term Debt	280,500,000	100,000,000	100,000,000				200,000,000	100,000,000
Capital lease obligations	7,123,000	7,179,000
Capital lease obligations, current	$ 3,281,000	$ 2,887,000
Aggregate repurchase obligation, amount, percentage					15.00%