Investment Securities AFS and HTM Securities Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Investment securities available for sale:
Amortized cost	$ 5,368,493	$ 5,368,259
Gross unrealized gains	76,330	85,085
Gross unrealized losses	(36,825)	(56,532)
Fair value	5,407,998	5,396,812
Investment securities held to maturity:
Amortized cost	532,382	404,455
Gross unrealized gains	4,360	9,444
Gross unrealized losses	(6,288)	(832)
Fair value	530,454	413,067
US Treasury Securities [Member]
Investment securities available for sale:
Amortized cost	999	999
Gross unrealized gains	2	0
Gross unrealized losses	0	(1)
Fair value	1,001	998
Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Amortized cost	451,577	560,839
Gross unrealized gains	18,576	21,869
Gross unrealized losses	(50)	(29)
Fair value	470,103	582,679
Investment securities held to maturity:
Amortized cost	532,382	404,455
Gross unrealized gains	4,360	9,444
Gross unrealized losses	(6,288)	(832)
Fair value	530,454	413,067
Federal National Mortgage Association Certificates and Obligations (FNMA) and Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Investment securities available for sale:
Amortized cost	2,207,339	3,534,240
Gross unrealized gains	52,006	59,640
Gross unrealized losses	(7,718)	(30,423)
Fair value	2,251,627	3,563,457
Government National Mortgage Association (GNMA) [Member]
Investment securities available for sale:
Amortized cost	905,728	165,863
Gross unrealized gains	1,876	1,596
Gross unrealized losses	(5,520)	(127)
Fair value	902,084	167,332
Private Label [Member]
Investment securities available for sale:
Amortized cost	1,926	2,297
Gross unrealized gains	1	7
Gross unrealized losses	(10)	(10)
Fair value	1,917	2,294
GNMA commercial mortgage-related securities [Member]
Investment securities available for sale:
Amortized cost	1,794,286	1,097,913
Gross unrealized gains	3,803	1,922
Gross unrealized losses	(23,527)	(25,942)
Fair value	1,774,562	1,073,893
Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Amortized cost	6,638	6,108
Gross unrealized gains	66	51
Gross unrealized losses	0	0
Fair value	$ 6,704	$ 6,159

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

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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