Investment Securities Schedule of Amortized Cost and Fair Values of Debt Securities by Contractual Maturities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013
Statement of Investments [Line Items]
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0
Held-to-maturity Securities, Debt Maturities, Next Twelve Months, Fair Value	0
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	45,346
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	45,470
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	0
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Fair Value	0
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Amortized Cost Basis	63,113
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Fair Value	66,924
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	0
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Fair Value	0
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	197,964
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Fair Value	201,552
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	0
Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value	0
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	265,638
Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value	243,713
Held to Maturity Debt Securities, Before Securities Without Single Maturity	0
Held to Maturity, Debt Securities Fair Value, Before Securities Without Single Maturity	0
Available for Sale Securities, Debt Securities, Amortized Cost, Before Securities Without Debt Maturities	572,061
Available for Sale Securities, Debt Maturities, Before Securities Without Single Maturities	557,659
Held to Maturity Securities, Amortized Cost	206
Held-to-maturity Securities, Debt Maturities, Fair Value	224
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis	2,595,106
Available for Sale, Estimated Fair Value	2,554,866
Collateralized Mortgage Backed Securities [Member]
Statement of Investments [Line Items]
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Net Carrying Amount	206
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	224
Collateralized Mortgage Obligations [Member]
Statement of Investments [Line Items]
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Net Carrying Amount	0
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	0
Collateralized Mortgage Backed Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	909,292
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	914,230
Collateralized Mortgage Obligations [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	1,113,753
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	$ 1,082,977