Investment Securities, AFS and HTM Securities Amortized Costs and Fair Values (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Investment securities available for sale:
Amortized Cost	$ 4,742,690	$ 4,984,867
Gross Unrealized Gains	66,577	35,684
Gross Unrealized Losses	(7,501)	(53,137)
Fair Value	4,801,766	4,967,414
Investment securities held to maturity:
Amortized Cost	1,236,140	1,168,230
Gross Unrealized Gains	42,767	17,505
Gross Unrealized Losses	(52)	(1,293)
Fair Value	1,278,855	1,184,442
US Treasury Securities [Member]
Investment securities available for sale:
Amortized Cost	1,000	999
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	(2)
Fair Value	1,001	997
Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities held to maturity:
Amortized Cost	1,111,868	1,043,767
Gross Unrealized Gains	40,280	16,803
Gross Unrealized Losses	(15)	(339)
Fair Value	1,152,133	1,060,231
Private Label [Member]
Investment securities available for sale:
Amortized Cost	1,429	1,722
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(19)	(14)
Fair Value	1,410	1,709
Investment securities held to maturity:
Amortized Cost	0
Fair Value	0
GNMA Commercial Mortgage-Related Securities [Member]
Investment securities available for sale:
Amortized Cost	2,124,491	1,982,477
Gross Unrealized Gains	9,912	1,334
Gross Unrealized Losses	(7,482)	(28,501)
Fair Value	2,126,921	1,955,310
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	4,718
Gross Unrealized Gains	91	51
Gross Unrealized Losses	0	0
Fair Value	4,809	4,769
FNMA and FHLMC [Member] \| Residential Related Securities [Member]
Investment securities available for sale:
Amortized Cost	956,834	1,388,995
Gross Unrealized Gains	33,545	33,791
Gross Unrealized Losses	0	(8,160)
Fair Value	990,379	1,414,626
Investment securities held to maturity:
Amortized Cost	39,019	41,469
Gross Unrealized Gains	977	513
Gross Unrealized Losses	(32)	(645)
Fair Value	39,964	41,337
GNMA [Member] \| Residential Related Securities [Member]
Investment securities available for sale:
Amortized Cost	1,654,218	1,605,956
Gross Unrealized Gains	23,028	507
Gross Unrealized Losses	0	(16,460)
Fair Value	1,677,246	1,590,003
Investment securities held to maturity:
Amortized Cost	85,253	82,994
Gross Unrealized Gains	1,510	189
Gross Unrealized Losses	(5)	(309)
Fair Value	$ 86,758	$ 82,874

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

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