Annual report pursuant to Section 13 and 15(d)

Available-for-Sale Securities, at Fair Value (Details)

v2.4.1.9
Available-for-Sale Securities, at Fair Value (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value $ 14,341,102us-gaap_AvailableForSaleSecurities $ 12,256,727us-gaap_AvailableForSaleSecurities
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value 2,418,546us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember 		2,977,291us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value 6,768,875us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember 		4,435,820us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value 2,104,896us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember 		2,084,298us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value $ 3,048,785us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember 		$ 2,759,318us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember