Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 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	4,809,893	$ 4,984,867
Fair Value
Available for Sale, Due in one year or less	4,535
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	5,735
Investment securities available for sale, at fair value	$ 4,846,088	4,967,414
Ratio of Fair Value to Amortized Cost	100.80%
Amortized Cost
Held to Maturity, Due in one year or less	$ 38,786
Held to Maturity, Due after one year through five years	250,221
Held to Maturity, Due after five years through ten years	234,104
Held to Maturity, Due after ten years	605,945
Held to Maturity, Debt Securities, Amortized Cost Basis	1,129,056
Held to Maturity Amortized Cost	1,253,494	1,168,230
Fair Value
Held to Maturity, Due in one year or less	27,004
Held to Maturity, Due after one year through five years	260,817
Held to Maturity, Due after five years through ten years	243,746
Held to Maturity, Due after ten years	629,153
Held to Maturity, Securities, Debt Securities	1,160,720
Held to Maturity, Total debt securities	$ 1,287,830	1,184,442
Ratio of Fair Value to Amortized Cost	102.70%
Private-label
Amortized Cost
Investment securities available for sale, amortized cost	$ 1,215	1,722
Fair Value
Investment securities available for sale, at fair value	1,200	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	2,121,913	1,982,477
Fair Value
Investment securities available for sale, at fair value	2,114,669	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	95
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	882,951	1,388,995
Fair Value
Investment securities available for sale, at fair value	912,860	1,414,626
Amortized Cost
Held to Maturity Amortized Cost	38,297	41,469
Fair Value
Held to Maturity, Total debt securities	39,290	41,337
GNMA [Member] \| Residential Related Securities [Member]
Amortized Cost
Investment securities available for sale, amortized cost	1,798,096	1,605,956
Fair Value
Investment securities available for sale, at fair value	1,811,529	1,590,003
Amortized Cost
Held to Maturity Amortized Cost	86,141	82,994
Fair Value
Held to Maturity, Total debt securities	$ 87,820	$ 82,874

Held-to-maturity Debt Securities, Amortized Cost Basis

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