Investment Securities, AFS and HTM Securities Amortized Costs and Fair Values (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Investment securities available for sale:
Amortized Cost	$ 4,984,867	$ 5,368,259
Gross Unrealized Gains	35,684	85,085
Gross Unrealized Losses	(53,137)	(56,532)
Fair Value	4,967,414	5,396,812
Investment securities held to maturity:
Amortized Cost	1,168,230	404,455
Gross Unrealized Gains	17,505	9,444
Gross Unrealized Losses	(1,293)	(832)
Fair Value	1,184,442	413,067
US Treasury Securities [Member]
Investment securities available for sale:
Amortized Cost	999	999
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	(1)
Fair Value	997	998
Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Amortized Cost		560,839
Gross Unrealized Gains		21,869
Gross Unrealized Losses		(29)
Fair Value		582,679
Investment securities held to maturity:
Amortized Cost	1,043,767	404,455
Gross Unrealized Gains	16,803	9,444
Gross Unrealized Losses	(339)	(832)
Fair Value	1,060,231	413,067
Private Label [Member]
Investment securities available for sale:
Amortized Cost	1,722	2,297
Gross Unrealized Gains	1	7
Gross Unrealized Losses	(14)	(10)
Fair Value	1,709	2,294
Investment securities held to maturity:
Amortized Cost	0
Fair Value	0
GNMA Commercial Mortgage-Related Securities [Member]
Investment securities available for sale:
Amortized Cost	1,982,477	1,097,913
Gross Unrealized Gains	1,334	1,922
Gross Unrealized Losses	(28,501)	(25,942)
Fair Value	1,955,310	1,073,893
Investment securities held to maturity:
Amortized Cost	0
Fair Value	0
Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Amortized Cost	4,718	6,108
Gross Unrealized Gains	51	51
Gross Unrealized Losses	0	0
Fair Value	4,769	6,159
FNMA and FHLMC [Member] \| Residential Related Securities [Member]
Investment securities available for sale:
Amortized Cost	1,388,995	3,534,240
Gross Unrealized Gains	33,791	59,640
Gross Unrealized Losses	(8,160)	(30,423)
Fair Value	1,414,626	3,563,457
Investment securities held to maturity:
Amortized Cost	41,469
Gross Unrealized Gains	513
Gross Unrealized Losses	(645)
Fair Value	41,337
GNMA [Member] \| Residential Related Securities [Member]
Investment securities available for sale:
Amortized Cost	1,605,956	165,863
Gross Unrealized Gains	507	1,596
Gross Unrealized Losses	(16,460)	(127)
Fair Value	1,590,003	$ 167,332
Investment securities held to maturity:
Amortized Cost	82,994
Gross Unrealized Gains	189
Gross Unrealized Losses	(309)
Fair Value	$ 82,874

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

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