Fair Value Measurements Details of Book Value and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Available for sale investment securities		$ 2,440,492	$ 2,323,371
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and Cash Equivalents		100,455	105,702
Interest-Rate Deposits with Other Banks		322,218	358,130
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure		65,106	64,953
Loans Held-for-sale	[1]	33,980	17,522
Available for sale investment securities	[1]	2,440,492	2,323,371
Loans, net of unearned income	[1]	13,244,230	13,111,716
Accrued Interest Receivable		41,193	41,818
Other Financial Assets	[1]	157,792	169,764
Demand and Savings Deposit Liabilities, Fair Value Disclosure		10,501,956	10,296,055
Time Deposit Liabilities, Fair Value Disclosure		3,003,753	3,071,451
Short-term borrowings		409,035	329,719
Accrued interest payable		15,172	18,045
Other Financial Liabilities	[1]	175,220	172,786
Federal Home Loan Bank Advances And Debt Long Term, Fair Value Disclosre		1,132,641	1,139,413
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and Cash Equivalents		100,455	105,702
Interest-Rate Deposits with Other Banks		322,218	358,130
Investment in Federal Home Loan Bank Stock, Fair Value Disclosure		65,106	64,953
Loans Held-for-sale	[1]	33,980	17,522
Available for sale investment securities	[1]	2,440,492	2,323,371
Loans, net of unearned income	[1]	13,129,521	13,030,543
Accrued Interest Receivable		41,193	41,818
Other Financial Assets	[1]	157,792	169,764
Demand and Savings Deposit Liabilities, Fair Value Disclosure		10,501,956	10,296,055
Time Deposit Liabilities, Fair Value Disclosure		2,999,352	3,069,883
Short-term borrowings		409,035	329,719
Accrued interest payable		15,172	18,045
Other Financial Liabilities	[1]	175,220	172,786
Federal Home Loan Bank Advances And Debt Long Term, Fair Value Disclosre		$ 1,152,810	$ 1,142,980

[1] These financial instruments, or certain financial instruments within these categories, are measured at fair value on the Corporation’s consolidated balance sheets. Descriptions of the fair value determinations for these financial instruments are disclosed above.