Fair Value of Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	$ 3,290,850	$ 3,367,557
Loans Held for Sale	24,015	21,374
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	339,403	470,535
Other Assets	13,129	12,566
Total Assets Measured at Fair Value on a Recurring Basis	352,532	483,101
Significant Other Observable Inputs (Level 2)
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	2,951,447	2,897,022
Loans Held for Sale	24,015	21,374
Derivatives	499	229
Total Assets Measured at Fair Value on a Recurring Basis	2,975,961	2,918,625
Liabilites:
Derivatives	382	1,185
Total Liabilities Measured at Fair Value on a Recurring Basis	382	1,185
Significant Other Unobservable Inputs (Level 3)
Investment Securities Available-for-Sale:
Mortgage Servicing Rights	4,436	4,761
Derivatives	34,899	42,381
Total Assets Measured at Fair Value on a Recurring Basis	39,335	47,142
Liabilites:
Derivatives	29,921	32,441
Total Liabilities Measured at Fair Value on a Recurring Basis	29,921	32,441
Total
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	3,290,850	3,367,557
Loans Held for Sale	24,015	21,374
Mortgage Servicing Rights	4,436	4,761
Other Assets	13,129	12,566
Derivatives	35,398	42,610
Total Assets Measured at Fair Value on a Recurring Basis	3,367,828	3,448,868
Liabilites:
Derivatives	30,303	33,626
Total Liabilities Measured at Fair Value on a Recurring Basis	30,303	33,626
Debt Securities Issued by the U.S. Treasury and Government Agencies
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	724,359	869,989
Debt Securities Issued by the U.S. Treasury and Government Agencies \| Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	339,403	470,535
Debt Securities Issued by the U.S. Treasury and Government Agencies \| Significant Other Observable Inputs (Level 2)
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	384,956	399,454
Debt Securities Issued by the U.S. Treasury and Government Agencies \| Total
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	724,359	869,989
Debt Securities Issued by States and Political Subdivisions
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	823,236	782,411
Debt Securities Issued by States and Political Subdivisions \| Significant Other Observable Inputs (Level 2)
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	823,236	782,411
Debt Securities Issued by States and Political Subdivisions \| Total
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	823,236	782,411
Debt Securities Issued by Corporations
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	188,556	84,434
Debt Securities Issued by Corporations \| Significant Other Observable Inputs (Level 2)
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	188,556	84,434
Debt Securities Issued by Corporations \| Total
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	188,556	84,434
Residential Mortgage-Backed Securities issued by U.S. government agencies
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	944,362	1,068,660
Residential Mortgage-Backed Securities issued by U.S. government agencies \| Significant Other Observable Inputs (Level 2)
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	944,362	1,068,660
Residential Mortgage-Backed Securities issued by U.S. government agencies \| Total
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	944,362	1,068,660
Residential Mortgage-Backed Securities Issued by U.S. Government Sponsored Enterprises
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	33,398	37,298
Residential Mortgage-Backed Securities Issued by U.S. Government Sponsored Enterprises \| Significant Other Observable Inputs (Level 2)
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	33,398	37,298
Residential Mortgage-Backed Securities Issued by U.S. Government Sponsored Enterprises \| Total
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	33,398	37,298
Commercial Mortgage-Backed Securities Issued by Government Agencies
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	576,939	524,765
Commercial Mortgage-Backed Securities Issued by Government Agencies \| Significant Other Observable Inputs (Level 2)
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	576,939	524,765
Commercial Mortgage-Backed Securities Issued by Government Agencies \| Total
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	576,939	524,765
Mortgage-Backed Securities
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	1,554,699	1,630,723
Mortgage-Backed Securities \| Significant Other Observable Inputs (Level 2)
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	1,554,699	1,630,723
Mortgage-Backed Securities \| Total
Investment Securities Available-for-Sale:
Total Investment Securities Available-for-Sale	$ 1,554,699	$ 1,630,723

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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The aggregate carrying amount of loans receivable that will be sold to other entities. Includes mortgage and all other loans (collectively, loans) not classified as held for investment. Such loans are stated at the lower of cost or market, or elected fair value. Mortgage loans exclude mortgage-backed securities which are considered a debt security (other loan).

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