Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Entity Information [Line Items]
Notes payable	$ 90.0	$ 7.9
Interest Costs Incurred, Capitalized	0.2	0.1	0
Unrealized gain (losses) on securities, net of reversals	0.8	(6.3)	(4.9)
Deferred income tax expense (benefit)	(7.1)	(28.3)	(8.7)
Concentration Risk, Percentage	45.70%	48.20%	49.00%
Amortization of Financing Costs and Discounts	1.5	2.6	3.1
Maximum [Member]
Entity Information [Line Items]
Equity Method Investment, Ownership Percentage	50.00%
Percentage Used To Determine Noncontrolling Interest Presentation	1.00
Minimum [Member]
Entity Information [Line Items]
Equity Method Investment, Ownership Percentage	20.00%
Percentage Used To Determine Noncontrolling Interest Presentation	0.50
Home Depot [Member]
Entity Information [Line Items]
Concentration Risk, Percentage	10.40%
Taiga [Member]
Entity Information [Line Items]
Concentration Risk, Percentage			10.90%
Non Recourse Notes Payable 2018 [Member]
Entity Information [Line Items]
Notes payable	368.7	368.7
Swap [Member]
Entity Information [Line Items]
Unrealized gain (losses) on securities, net of reversals	1.2	0.7
Deferred income tax expense (benefit)	0.2
Deferred Loss on Early Extinguishment of Debt [Member]
Entity Information [Line Items]
Write off of Deferred Debt Issuance Cost	4.5
Senior Notes 2018 [Member]
Entity Information [Line Items]
Debt Instrument Collateral Amount	$ 410.0