Investment Securities, AFS and HTM Securities Amortized Costs and Fair Values (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investment securities available for sale:
Amortized Cost	$ 3,713,769	$ 4,724,895
Gross Unrealized Gains	15,957	19,132
Gross Unrealized Losses	(42,256)	(63,801)
Fair Value	3,687,470	4,680,226
Investment securities held to maturity:
Amortized Cost	2,255,395	1,273,536
Gross Unrealized Gains	27,208	4,523
Gross Unrealized Losses	(19,281)	(13,385)
Fair Value	2,263,322	1,264,674
US Treasury Securities
Investment securities available for sale:
Amortized Cost	1,004	1,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	0
Fair Value	1,002	1,000
Obligations of state and political subdivisions (municipal securities)
Investment securities held to maturity:
Amortized Cost	1,162,920	1,145,843
Gross Unrealized Gains	13,766	3,868
Gross Unrealized Losses	(4,320)	(12,036)
Fair Value	1,172,366	1,137,675
Private Label
Investment securities available for sale:
Amortized Cost	1,102	1,134
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(16)	(14)
Fair Value	1,086	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	1,443,501	2,064,508
Gross Unrealized Gains	74	356
Gross Unrealized Losses	(23,703)	(35,966)
Fair Value	1,419,872	2,028,898
Investment securities held to maturity:
Amortized Cost	575,383
Gross Unrealized Gains	8,964
Gross Unrealized Losses	(11,181)
Fair Value	573,166
Other Debt And Other Equity Securities
Investment securities available for sale:
Amortized Cost	4,718	4,718
Gross Unrealized Gains	116	105
Gross Unrealized Losses	(27)	(21)
Fair Value	4,807	4,802
FNMA and FHLMC \| Residential Related Securities
Investment securities available for sale:
Amortized Cost	534,058	625,234
Gross Unrealized Gains	13,873	17,298
Gross Unrealized Losses	(1,406)	(2,602)
Fair Value	546,525	639,930
Investment securities held to maturity:
Amortized Cost	43,575	37,697
Gross Unrealized Gains	430	439
Gross Unrealized Losses	(566)	(693)
Fair Value	43,439	37,443
GNMA \| Residential Related Securities
Investment securities available for sale:
Amortized Cost	1,729,386	2,028,301
Gross Unrealized Gains	1,894	1,372
Gross Unrealized Losses	(17,102)	(25,198)
Fair Value	1,714,178	2,004,475
Investment securities held to maturity:
Amortized Cost	473,517	89,996
Gross Unrealized Gains	4,048	216
Gross Unrealized Losses	(3,214)	(656)
Fair Value	$ 474,351	$ 89,556

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

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