Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Amortized Cost
Available for Sale, Due in one year or less	$ 1,000
Available for Sale, Due after one year through five years	4,703
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	5,703
Investment securities available for sale, amortized cost	3,829,984	$ 4,724,895
Fair Value
Available for Sale, Due in one year or less	1,000
Available for Sale, Due after one year through five years	4,675
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	5,675
Investment securities available for sale, at fair value	$ 3,801,699	4,680,226
Ratio of Fair Value to Amortized Cost	99.30%
Amortized Cost
Held to Maturity, Due in one year or less	$ 54,259
Held to Maturity, Due after one year through five years	222,037
Held to Maturity, Due after five years through ten years	281,559
Held to Maturity, Due after ten years	634,435
Held to Maturity, Debt Securities, Amortized Cost Basis	1,192,290
Held to Maturity Amortized Cost	2,233,579	1,273,536
Fair Value
Held to Maturity, Due in one year or less	48,123
Held to Maturity, Due after one year through five years	227,978
Held to Maturity, Due after five years through ten years	284,789
Held to Maturity, Due after ten years	642,067
Held to Maturity, Securities, Debt Securities	1,202,957
Held to Maturity, Total debt securities	$ 2,243,845	1,264,674
Ratio of Fair Value to Amortized Cost	100.50%
Private Label
Amortized Cost
Investment securities available for sale, amortized cost	$ 1,083	1,134
Fair Value
Investment securities available for sale, at fair value	1,072	1,121
Amortized Cost
Held to Maturity Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities	0
GNMA Commercial Mortgage-Related Securities
Amortized Cost
Investment securities available for sale, amortized cost	1,539,169	2,064,508
Fair Value
Investment securities available for sale, at fair value	1,513,077	2,028,898
Amortized Cost
Held to Maturity Amortized Cost	554,707
Fair Value
Held to Maturity, Total debt securities	553,149
Asset backed Securities
Amortized Cost
Investment securities available for sale, amortized cost	108,590
Fair Value
Investment securities available for sale, at fair value	108,628
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	150
Amortized Cost
Held to Maturity Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities	0
FNMA and FHLMC \| Residential Related Securities
Amortized Cost
Investment securities available for sale, amortized cost	494,041	625,234
Fair Value
Investment securities available for sale, at fair value	505,261	639,930
Amortized Cost
Held to Maturity Amortized Cost	42,386	37,697
Fair Value
Held to Maturity, Total debt securities	42,446	37,443
GNMA \| Residential Related Securities
Amortized Cost
Investment securities available for sale, amortized cost	1,681,380	2,028,301
Fair Value
Investment securities available for sale, at fair value	1,667,836	2,004,475
Amortized Cost
Held to Maturity Amortized Cost	444,196	89,996
Fair Value
Held to Maturity, Total debt securities	$ 445,293	$ 89,556

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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