Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Amortized Cost
Available for Sale, Due in one year or less	$ 4,500
Available for Sale, Due after one year through five years	1,200
Available for Sale, Due after five years through ten years	0
Available for Sale, Due after ten years	0
Available for Sale, Total debt securities	5,700
Investment securities available for sale, amortized cost	4,742,690	$ 4,984,867
Fair Value
Available for Sale, Due in one year or less	4,538
Available for Sale, Due after one year through five years	1,200
Available for Sale, Due after five years through ten years	0
Available for Sale, Due after ten years	0
Available for Sale, Total debt securities	5,738
Investment securities available for sale, at fair value	$ 4,801,766	4,967,414
Ratio of Fair Value to Amortized Cost	101.20%
Amortized Cost
Held to Maturity, Due in one year or less	$ 38,985
Held to Maturity, Due after one year through five years	252,762
Held to Maturity, Due after five years through ten years	231,798
Held to Maturity, Due after ten years	588,323
Held to Maturity, Debt Securities, Amortized Cost Basis	1,111,868
Held to Maturity Amortized Cost	1,236,140	1,168,230
Fair Value
Held to Maturity, Due in one year or less	25,846
Held to Maturity, Due after one year through five years	265,059
Held to Maturity, Due after five years through ten years	242,887
Held to Maturity, Due after ten years	618,341
Held to Maturity, Securities, Debt Securities	1,152,133
Held to Maturity, Total debt securities	$ 1,278,855	1,184,442
Ratio of Fair Value to Amortized Cost	103.50%
Private Label [Member]
Amortized Cost
Investment securities available for sale, amortized cost	$ 1,429	1,722
Fair Value
Investment securities available for sale, at fair value	1,410	1,709
Amortized Cost
Held to Maturity Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities	0
GNMA Commercial Mortgage-Related Securities [Member]
Amortized Cost
Investment securities available for sale, amortized cost	2,124,491	1,982,477
Fair Value
Investment securities available for sale, at fair value	2,126,921	1,955,310
Amortized Cost
Held to Maturity Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities	0
Equity Securities [Member]
Amortized Cost
Investment securities available for sale, amortized cost	18
Fair Value
Investment securities available for sale, at fair value	72
Amortized Cost
Held to Maturity Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities	0
FNMA and FHLMC [Member] \| Residential Related Securities [Member]
Amortized Cost
Investment securities available for sale, amortized cost	956,834	1,388,995
Fair Value
Investment securities available for sale, at fair value	990,379	1,414,626
Amortized Cost
Held to Maturity Amortized Cost	39,019	41,469
Fair Value
Held to Maturity, Total debt securities	39,964	41,337
GNMA [Member] \| Residential Related Securities [Member]
Amortized Cost
Investment securities available for sale, amortized cost	1,654,218	1,605,956
Fair Value
Investment securities available for sale, at fair value	1,677,246	1,590,003
Amortized Cost
Held to Maturity Amortized Cost	85,253	82,994
Fair Value
Held to Maturity, Total debt securities	$ 86,758	$ 82,874

Held-to-maturity Debt Securities, Amortized Cost Basis

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