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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Variable interest rate in effect as of the balance sheet date related to the interest rate derivative.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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FAIR VALUE DISCLOSURES (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage rate deduction to determine the fair value of other real estate owned (in hundredths)	7.00%
Available-for-sale securities [Abstract]
Available-for-sale securities	$ 2,016,373	$ 2,082,329	$ 2,194,373
Mortgage servicing rights	$ 50,544	57,268	49,190	$ 51,296
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative interest rate	1.80%
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative interest rate	4.00%
Carrying Value [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	$ 2,016,373	2,082,329
Loans held for sale	150,046	157,907
Fair Value [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	2,016,373	2,082,329
Loans held for sale	150,046	157,907
Fair Value, Measurements, Recurring [Member]
Available-for-sale securities [Abstract]
Mortgage servicing rights	50,544		49,190
Derivative instruments	23,479		27,145
Loans held for sale	150,046		186,510
Total	2,240,442		2,457,218
Liabilities [Abstract]
Derivative instruments	19,089		23,724
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Available-for-sale securities [Abstract]
Total	810		1,214
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Available-for-sale securities [Abstract]
Loans held for sale	150,046		186,510
Total	2,165,609		2,379,669
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Available-for-sale securities [Abstract]
Mortgage servicing rights	50,544		49,190
Derivative instruments	23,479		27,145
Total	74,023		76,335
Liabilities [Abstract]
Derivative instruments	19,089		23,724
US Government Agencies [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	1,196,167	1,244,640	1,286,981
US Government Agencies [Member] \| Fair Value, Measurements, Recurring [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	1,196,167		1,286,981
US Government Agencies [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	1,196,167		1,286,981
Government Agency Issued Residential Mortgage-Backed Securities [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	189,741	140,540	200,381
Government Agency Issued Residential Mortgage-Backed Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	189,741		200,381
Government Agency Issued Residential Mortgage-Backed Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	189,741		200,381
Government Agency Issued Commercial Mortgage-Backed Securities [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	207,908	260,693	227,409
Government Agency Issued Commercial Mortgage-Backed Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	207,908		227,409
Government Agency Issued Commercial Mortgage-Backed Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	207,908		227,409
Obligations Of States And Political Subdivisions [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	408,537	417,499	471,539
Obligations Of States And Political Subdivisions [Member] \| Fair Value, Measurements, Recurring [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	408,537		471,539
Obligations Of States And Political Subdivisions [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	408,537		471,539
Other [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	14,020	$ 18,957	8,063
Other [Member] \| Fair Value, Measurements, Recurring [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	14,020		8,063
Other [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	810		1,214
Other [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Available-for-sale securities [Abstract]
Available-for-sale securities	$ 13,210		$ 6,849