Estimated Fair Values (Estimated Fair Values For Certain Financial Assets And Financial Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 495,901		$ 604,182
Overnight investments	2,458,923		1,724,919
Investment securities available for sale	7,045,109		7,171,917
Investment securities held to maturity	441		518
Loans held for sale	66,508		63,696
Loans and Leases Receivable, Net Amount	18,886,204		18,564,999
FDIC Indemnification Asset	21,340		28,701		74,784	93,397
Income earned not collected	63,165		57,254
Mortgage servicing rights	16,436		16,688		0	16
Deposits	26,300,830		25,678,577
FDIC loss share payable	118,645		116,535
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	495,901		604,182
Overnight investments	2,458,923		1,724,919
Investment securities available for sale	7,045,109		7,171,917
Investment securities held to maturity	441		518
Loans held for sale	66,508		63,696
Loans and Leases Receivable, Net Amount	18,886,204		18,564,999
FDIC Indemnification Asset	21,340	[1]	28,701	[1]
Income earned not collected	63,165		57,254
Stock issued by Federal Home Loan Bank	30,291		39,113
Preferred stock and other acquired financial assets	13,689		13,689
Mortgage servicing rights	16,436		16,688
Deposits	26,300,830		25,678,577
Short-term borrowings	941,850		987,184
Long-term obligations	468,180		351,320
FDIC loss share payable	118,645		116,535
Accrued interest payable	8,370		8,194
Interest rate swap	3,761		4,337
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	495,901		604,182
Overnight investments	2,458,923		1,724,919
Investment securities available for sale	7,045,109		7,171,917
Investment securities held to maturity	459		544
Loans held for sale	66,508		63,696
Loans and Leases Receivable, Net Amount	18,359,306		18,046,497
FDIC Indemnification Asset	14,407	[1]	18,218	[1]
Income earned not collected	63,165		57,254
Stock issued by Federal Home Loan Bank	30,291		39,113
Preferred stock and other acquired financial assets	14,688		14,708
Mortgage servicing rights	16,719		16,736
Deposits	25,718,225		25,164,683
Short-term borrowings	941,850		987,184
Long-term obligations	486,960		367,732
FDIC loss share payable	126,113		122,168
Accrued interest payable	8,370		8,194
Interest rate swap	$ 3,761		$ 4,337

[1] The fair value of the FDIC receivable excludes receivable related to accretable yield to be amortized in prospective periods.