Estimated Fair Values (Estimated Fair Values For Certain Financial Assets And Financial Liabilities) (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		$ 495,705		$ 534,086
Overnight investments		2,997,086		2,063,132
Investment securities available for sale		6,384,815		6,861,293
Investment securities held to maturity		125		255
Loans held for sale		95,910		59,766
Loans and Leases Receivable, Net Amount		21,085,030		20,033,774
FDIC Indemnification Asset		3,108	$ 5,281	4,054	$ 9,276	$ 5,808	$ 28,701
Income earned not collected		74,933		70,036
Mortgage servicing rights		17,730	$ 16,824	19,351	$ 19,327	$ 18,162	$ 16,688
Deposits		27,925,253		26,930,755
FDIC loss share payable		95,779		126,453
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		495,705		534,086
Overnight investments		2,997,086		2,063,132
Investment securities available for sale		6,384,815		6,861,293
Investment securities held to maturity		125		255
Loans held for sale		95,910		59,766
Loans and Leases Receivable, Net Amount		21,085,030		20,033,774
FDIC Indemnification Asset	[1]	3,108		4,054
Income earned not collected		74,933		70,036
Stock issued by Federal Home Loan Bank		43,495		37,511
Mortgage servicing rights		17,730		19,351
Deposits		27,925,253		26,930,755
Short-term borrowings		730,214		594,733
Long-term obligations		840,266		704,155
FDIC loss share payable		95,779		126,453
Accrued interest payable		4,051		5,713
Interest rate swap		0		1,429
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		495,705		534,086
Overnight investments		2,997,086		2,063,132
Investment securities available for sale		6,384,815		6,861,293
Investment securities held to maturity		133		265
Loans held for sale		95,910		59,766
Loans and Leases Receivable, Net Amount		20,531,249		19,353,325
FDIC Indemnification Asset	[1]	3,108		4,054
Income earned not collected		74,933		70,036
Stock issued by Federal Home Loan Bank		43,495		37,511
Mortgage servicing rights		17,965		19,495
Deposits		27,913,775		26,164,472
Short-term borrowings		730,214		594,733
Long-term obligations		870,386		718,102
FDIC loss share payable		101,117		131,894
Accrued interest payable		4,051		5,713
Interest rate swap		$ 0		$ 1,429

[1] (1) The interest rate swap agreement expired in June 2016.