Debt Obligations Securitization Debt (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together [Line Items]
Debt Balance	$ 989,206		$ 1,049,478
Repurchase Option Percentage	10.00%
Securitization Debt [Member]
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together [Line Items]
Debt Balance	569,884		677,118
Gross Receivables Pledged	735,156		873,231
Cash Reserve	26,700		26,700
2010-1 [Member] | Securitization Debt [Member]
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together [Line Items]
Debt Balance	16,037		23,036
Gross Receivables Pledged	40,958		55,525
Cash Reserve	4,500		4,500
Interest Rate	3.60%	[1]	3.60%	[1]
2011-1 [Member] | Securitization Debt [Member]
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together [Line Items]
Debt Balance	48,398		60,335
Gross Receivables Pledged	67,170		84,198
Cash Reserve	4,200		4,200
Interest Rate	3.00%	[1]	3.00%	[1]
2011-2 [Member] | Securitization Debt [Member]
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together [Line Items]
Debt Balance	69,436		84,977
Gross Receivables Pledged	84,419		103,779
Cash Reserve	4,500		4,500
Interest Rate	2.90%	[1]	2.90%	[1]
2011-3 [Member] | Securitization Debt [Member]
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together [Line Items]
Debt Balance	106,570		130,347
Gross Receivables Pledged	129,943		159,068
Cash Reserve	4,500		4,500
Interest Rate	3.90%	[1]	3.90%	[1]
2012-1 [Member] | Securitization Debt [Member]
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together [Line Items]
Debt Balance	145,443		170,198
Gross Receivables Pledged	188,752		219,252
Cash Reserve	4,500		4,500
Interest Rate	3.50%	[1]	3.50%	[1]
2012-2 [Member] | Securitization Debt [Member]
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together [Line Items]
Debt Balance	184,000		208,225
Gross Receivables Pledged	223,914		251,409
Cash Reserve	$ 4,500		$ 4,500
Interest Rate	2.90%	[1]	2.90%	[1]

[1] These rates represent the original duration weighted average rates of the outstanding asset-backed securities.