Investment Securities, AFS and HTM Securities Amortized Costs and Fair Values (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Investment securities available for sale:
Amortized Cost	$ 3,829,984	$ 4,724,895
Gross Unrealized Gains	15,552	19,132
Gross Unrealized Losses	(43,837)	(63,801)
Fair Value	3,801,699	4,680,226
Investment securities held to maturity:
Amortized Cost	2,233,579	1,273,536
Gross Unrealized Gains	28,951	4,523
Gross Unrealized Losses	(18,685)	(13,385)
Fair Value	2,243,845	1,264,674
US Treasury Securities
Investment securities available for sale:
Amortized Cost	1,003	1,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	0
Fair Value	1,001	1,000
Obligations of state and political subdivisions (municipal securities)
Investment securities held to maturity:
Amortized Cost	1,192,290	1,145,843
Gross Unrealized Gains	14,525	3,868
Gross Unrealized Losses	(3,858)	(12,036)
Fair Value	1,202,957	1,137,675
Private Label
Investment securities available for sale:
Amortized Cost	1,083	1,134
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(11)	(14)
Fair Value	1,072	1,121
Investment securities held to maturity:
Amortized Cost	0
Fair Value	0
GNMA Commercial Mortgage-Related Securities
Investment securities available for sale:
Amortized Cost	1,539,169	2,064,508
Gross Unrealized Gains	73	356
Gross Unrealized Losses	(26,165)	(35,966)
Fair Value	1,513,077	2,028,898
Investment securities held to maturity:
Amortized Cost	554,707
Gross Unrealized Gains	10,250
Gross Unrealized Losses	(11,808)
Fair Value	553,149
Asset backed Securities
Investment securities available for sale:
Amortized Cost	108,590
Gross Unrealized Gains	63
Gross Unrealized Losses	(25)
Fair Value	108,628
Investment securities held to maturity:
Amortized Cost	0
Fair Value	0
Other Debt And Other Equity Securities
Investment securities available for sale:
Amortized Cost	4,718	4,718
Gross Unrealized Gains	132	105
Gross Unrealized Losses	(26)	(21)
Fair Value	4,824	4,802
FNMA and FHLMC \| Residential Related Securities
Investment securities available for sale:
Amortized Cost	494,041	625,234
Gross Unrealized Gains	12,780	17,298
Gross Unrealized Losses	(1,560)	(2,602)
Fair Value	505,261	639,930
Investment securities held to maturity:
Amortized Cost	42,386	37,697
Gross Unrealized Gains	464	439
Gross Unrealized Losses	(404)	(693)
Fair Value	42,446	37,443
GNMA \| Residential Related Securities
Investment securities available for sale:
Amortized Cost	1,681,380	2,028,301
Gross Unrealized Gains	2,504	1,372
Gross Unrealized Losses	(16,048)	(25,198)
Fair Value	1,667,836	2,004,475
Investment securities held to maturity:
Amortized Cost	444,196	89,996
Gross Unrealized Gains	3,712	216
Gross Unrealized Losses	(2,615)	(656)
Fair Value	$ 445,293	$ 89,556

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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