Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investment securities available for sale:
Total investment securities available for sale	$ 4,950,317	$ 4,926,758
Trading Assets	65,014	70,711
Fair Value, Inputs, Level 1 [Member]
Investment securities available for sale:
Total investment securities available for sale	2,994	3,845
Fair Value, Inputs, Level 2 [Member]
Investment securities available for sale:
Total investment securities available for sale	4,946,812	4,922,433
Fair Value, Inputs, Level 3 [Member]
Investment securities available for sale:
Total investment securities available for sale	511	480
Fair Value, Measurements, Recurring [Member]
Investment securities available for sale:
Total investment securities available for sale	4,950,317	4,926,758
Trading Assets	75,919	82,125
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	76,716	80,110
Fair Value, Measurements, Recurring [Member] \| US Treasury Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	1,004	1,004
Fair Value, Measurements, Recurring [Member] \| Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Total investment securities available for sale	777,287	801,188
Fair Value, Measurements, Recurring [Member] \| Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	3,786,760	3,804,304
Fair Value, Measurements, Recurring [Member] \| Commercial Mortgage Backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	300,639	228,166
Fair Value, Measurements, Recurring [Member] \| Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	84,627	92,096
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Investment securities available for sale:
Total investment securities available for sale	2,994	3,845
Trading Assets	0	0
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| US Treasury Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	1,004	1,004
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Commercial Mortgage Backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	1,990	2,841
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Investment securities available for sale:
Total investment securities available for sale	4,946,812	4,922,433
Trading Assets	70,651	74,331
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	75,873	79,963
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US Treasury Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Total investment securities available for sale	777,287	801,188
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	3,786,760	3,804,304
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Commercial Mortgage Backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	300,639	228,166
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	82,126	88,775
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Investment securities available for sale:
Total investment securities available for sale	511	480
Trading Assets	5,268	7,794
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	843	147
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| US Treasury Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Commercial Mortgage Backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	$ 511	$ 480

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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- Definition

Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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