Held-to-Maturity Securities (Interest Rate Payment Terms) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	$ 5,189,118	$ 5,241,312
Collateralized Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	5,155,745	5,202,553
Fixed Interest Rate [Member] | Mortgage Passthrough Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	380	454
Fixed Interest Rate [Member] | Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	883	1,050
Adjustable Interest Rate [Member] | Held To Maturity Securities Other Than Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	33,373	38,759
Adjustable Interest Rate [Member] | Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	$ 5,154,482	$ 5,201,049