For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading. Such securities are reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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The total of financial instruments that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for debt and equity securities formerly categorized as available-for-sale or held-to-maturity which the entity held as of the date it opted to account for such securities at fair value. An enterprise may also categorize such a security as trading without the intent to sell it in the near term assuming the decision to categorize the security as trading occurred at acquisition; this is the reason why the trading category of investments in debt and equity securities are bought and sold "principally" for sale in the near term. Transfers into and out of the trading category should be rare. Such financial instruments that are held as of the reporting date are measured at fair value with unrealized holding gains and losses (the difference between fair value and the previously reported carrying amount) included in earnings.

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Fair Value Measurements (Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring Basis) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Securities available for sale	$ 5,432,354	$ 5,157,470	$ 4,753,608
Trading account securities	14,517	15,101	15,833
U.S. Treasury [Member] \| Level 1 Inputs
Securities available for sale	794,285	987,031
Trading account securities	14,517	14,986
Residential Mortgage-Backed Securities [Member] \| Level 1 Inputs
Securities available for sale
States and Political Subdivisions [Member] \| Level 1 Inputs
Securities available for sale
Trading account securities
Other [Member] \| Level 1 Inputs
Securities available for sale
Level 1 Inputs \| Interest Rate Swaps, Caps and Floors [Member]
Derivative assets
Derivative liabilities
Level 1 Inputs \| Commodity and Foreign Exchange Derivatives [Member]
Derivative assets
Derivative liabilities	29	19
U.S. Treasury [Member] \| Level 2 Inputs
Securities available for sale
Trading account securities
Residential Mortgage-Backed Securities [Member] \| Level 2 Inputs
Securities available for sale	2,484,663	2,091,330
States and Political Subdivisions [Member] \| Level 2 Inputs
Securities available for sale	2,115,426	2,040,300
Trading account securities		115
Other [Member] \| Level 2 Inputs
Securities available for sale	37,980	38,809
Level 2 Inputs \| Interest Rate Swaps, Caps and Floors [Member]
Derivative assets	44,198	43,633
Derivative liabilities	61,549	63,299
Level 2 Inputs \| Commodity and Foreign Exchange Derivatives [Member]
Derivative assets	19,418	14,177
Derivative liabilities	19,187	14,082
U.S. Treasury [Member] \| Level 3 Inputs
Securities available for sale
Trading account securities
Residential Mortgage-Backed Securities [Member] \| Level 3 Inputs
Securities available for sale
States and Political Subdivisions [Member] \| Level 3 Inputs
Securities available for sale
Trading account securities
Other [Member] \| Level 3 Inputs
Securities available for sale
Level 3 Inputs \| Interest Rate Swaps, Caps and Floors [Member]
Derivative assets	298	1,090
Derivative liabilities
Level 3 Inputs \| Commodity and Foreign Exchange Derivatives [Member]
Derivative assets
Derivative liabilities
U.S. Treasury [Member]
Securities available for sale	794,285	987,031
Trading account securities	14,517	14,986
Residential Mortgage-Backed Securities [Member]
Securities available for sale	2,484,663	2,091,330
Other [Member]
Securities available for sale	37,980	38,809
Interest Rate Swaps, Caps and Floors [Member]
Derivative assets	44,496	44,723
Derivative liabilities	61,549	63,299
Commodity and Foreign Exchange Derivatives [Member]
Derivative assets	19,418	14,177
Derivative liabilities	19,216	14,101
States and Political Subdivisions [Member]
Securities available for sale	2,115,426	2,040,300
Trading account securities		$ 115