Assets and Liabilities Recorded at Fair Value on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
[EstimateOfFairValueFairValueDisclosureMember]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed securities	$ 380,560	$ 168,155
Margin Deposit Assets Fair Value Disclosure	2,682	227
Retained Interests	3,463	3,336
[FairValueInputsLevel1Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed securities	0	0
Margin Deposit Assets Fair Value Disclosure	2,682	227
Retained Interests	0	0
[FairValueInputsLevel2Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed securities	380,560	168,155
Margin Deposit Assets Fair Value Disclosure	0	0
Retained Interests	0	0
[FairValueInputsLevel3Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed securities	0	0
Margin Deposit Assets Fair Value Disclosure	0	0
Retained Interests	$ 3,463	$ 3,336