Estimated Fair Values (Estimated Fair Values For Certain Financial Assets And Financial Liabilities) (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		$ 457,758	$ 534,086
Overnight investments		2,871,105	2,063,132
Investment securities available for sale		6,687,289	6,861,293
Investment securities held to maturity		194	255
Loans held for sale		66,988	59,766
Loans and Leases Receivable, Net Amount		20,210,906	20,033,774
FDIC Indemnification Asset		7,474	4,054	$ 21,340	$ 28,701
Income earned not collected		73,518	70,036
Mortgage servicing rights		17,186	19,351	$ 16,436	$ 16,688
Deposits		27,365,245	26,930,755
FDIC loss share payable		128,243	126,453
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		457,758	534,086
Overnight investments		2,871,105	2,063,132
Investment securities available for sale		6,687,289	6,861,293
Investment securities held to maturity		194	255
Loans held for sale		66,988	59,766
Loans and Leases Receivable, Net Amount		20,210,906	20,033,774
FDIC Indemnification Asset	[1]	7,474	4,054
Income earned not collected		73,518	70,036
Stock issued by Federal Home Loan Bank		40,407	37,511
Mortgage servicing rights		17,186	19,351
Deposits		27,365,245	26,930,755
Short-term borrowings		689,236	594,733
Long-term obligations		779,087	704,155
FDIC loss share payable		128,243	126,453
Accrued interest payable		6,037	5,713
Interest rate swap		729	1,429
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		457,758	534,086
Overnight investments		2,871,105	2,063,132
Investment securities available for sale		6,687,289	6,861,293
Investment securities held to maturity		203	265
Loans held for sale		66,988	59,766
Loans and Leases Receivable, Net Amount		19,703,240	19,353,325
FDIC Indemnification Asset	[1]	7,474	4,054
Income earned not collected		73,518	70,036
Stock issued by Federal Home Loan Bank		40,407	37,511
Mortgage servicing rights		17,234	19,495
Deposits		26,904,946	26,164,472
Short-term borrowings		689,236	594,733
Long-term obligations		808,765	718,102
FDIC loss share payable		136,646	131,894
Accrued interest payable		6,037	5,713
Interest rate swap		$ 729	$ 1,429

[1] (1) At March 31, 2016 and December 31, 2015, the carrying value of the FDIC receivable approximates the fair value due to the short term nature of the majority of loss share agreements.