Income Taxes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current:
Federal	$ 146.9	$ 125.3	$ 115.4
State	25.1	21.3	19.5
Federal and state deferred	27.1	31.3	13.2
Change in valuation allowance, net	0.1	(0.2)	(0.1)
Adjustments and settlements	0.3	(0.6)	(2.0)
Income tax provision	199.5	177.1	146.0
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income tax provision at statutory rate	180.9	161.4	133.4
Non-deductible expenses (income), net	(0.2)	1.1	1.5
State income taxes, net of federal benefit	18.8	16.7	13.9
Income tax provision, excluding other reconciling items	199.5	179.2	148.8
Change in valuation allowance, net	0.1	(0.2)	(0.1)
Adjustments and settlements	0.3	(0.6)	(2.0)
Other, net	(0.4)	(1.3)	(0.7)
Income tax provision	199.5	177.1	146.0
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Income tax provision at statutory rate, %	35.00%	35.00%	35.00%
Non-deductible expenses (income), net, %	0.00%	0.20%	0.40%
State income taxes, net of federal benefit, %	3.60%	3.60%	3.60%
Income tax provision, excluding other reconciling items, %	38.60%	38.80%	39.00%
Change in valuation allowance, net, %	0.00%	0.00%	0.00%
Adjustments and settlements, %	0.00%	(0.20%)	(0.50%)
Other, net, %	0.00%	(0.20%)	(0.20%)
Income tax provision, %	38.60%	38.40%	38.30%
Deferred income tax assets:
Inventory	20.3	11.3
Receivable reserves	4.0	4.5
Warranty, chargeback and self - insurance liabilities	42.8	38.2
Other accrued liabilities	31.6	35.8
Stock-based compensation	20.6	18.8
Loss carryforwards—federal and state	13.8	14.3
Other, net	15.4	18.0
Total deferred income tax assets	148.5	140.9
Valuation allowance	(6.5)	(6.5)
Deferred income tax assets, net of valuation allowance	142.0	134.4
Deferred income tax liabilities:
Long-lived assets (intangibles assets and property)	(170.1)	(142.5)
Other, net	(16.6)	(9.4)
Total deferred income tax liabilities	(186.7)	(151.9)
Net deferred income tax assets (liabilities)	(44.7)	(17.5)
Deferred Tax Assets, Net, Classification [Abstract]
Deferred Tax Assets, Net, Current	44.7	41.8
Deferred Tax Assets, Net, Noncurrent		3.0
Deferred Tax Liabilities, Gross, Noncurrent		62.3
Deferred Tax Liabilities, Net, Noncurrent	89.4	62.3
Income taxes payable included in other current liabilities	3.2
Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]
Gross domestic state net operating and capital loss carryforwards	246.2
State tax credits	4.9
Deferred tax asset, loss carryforwards and tax credits	13.7
Valuation allowance related to loss carryforwards	6.5	6.5
Recognized net tax benefits related to adjustments and resolution of certain income tax matters		$ 1.3	$ 2.7