Estimated Fair Values (Estimated Fair Values For Certain Financial Assets And Financial Liabilities) (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		$ 546,444		$ 604,182
Overnight investments		2,368,132		1,724,919
Investment securities available for sale		6,690,578		7,171,917
Investment securities held to maturity		301		518
Loans held for sale		71,874		63,696
Loans and Leases Receivable, Net Amount		19,650,343		18,564,999
FDIC Indemnification Asset		9,276	$ 5,808	28,701	$ 45,140	$ 49,959	$ 93,397
Income earned not collected		67,368		57,254
Mortgage servicing rights		19,327	$ 18,162	16,688	$ 0	$ 0	$ 16
Deposits		26,719,375		25,678,577
FDIC loss share payable		124,038		116,535
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		546,444		604,182
Overnight investments		2,368,132		1,724,919
Investment securities available for sale		6,690,578		7,171,917
Investment securities held to maturity		301		518
Loans held for sale		71,874		63,696
Loans and Leases Receivable, Net Amount		19,650,343		18,564,999
FDIC Indemnification Asset	[1]	9,276		28,701
Income earned not collected		67,368		57,254
Stock issued by Federal Home Loan Bank		37,511		39,113
Mortgage servicing rights		19,327		16,688
Deposits		26,719,375		25,678,577
Short-term borrowings		759,757		987,184
Long-term obligations		705,418		351,320
FDIC loss share payable		124,038		116,535
Accrued interest payable		5,950		8,194
Interest rate swap		2,331		4,337
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks		546,444		604,182
Overnight investments		2,368,132		1,724,919
Investment securities available for sale		6,690,578		7,171,917
Investment securities held to maturity		314		544
Loans held for sale		71,874		63,696
Loans and Leases Receivable, Net Amount		19,038,274		18,046,497
FDIC Indemnification Asset	[1]	9,276		18,218
Income earned not collected		67,368		57,254
Stock issued by Federal Home Loan Bank		37,511		39,113
Mortgage servicing rights		22,358		16,736
Deposits		26,050,802		25,164,683
Short-term borrowings		759,757		987,184
Long-term obligations		722,180		367,732
FDIC loss share payable		131,711		122,168
Accrued interest payable		5,950		8,194
Interest rate swap		$ 2,331		$ 4,337

[1] (1) At September 30, 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. At December 31, 2014, the fair value of the FDIC receivable is estimated based on discounted future cash flows using current discount rates and excludes receivable related to accretable yield to be amortized in prospective periods.