FAIR VALUE (Details) (USD $)	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Dec. 31, 2011
Available-for-sale investment securities:
Total available-for-sale investment securities	$ 2,045,380,000				$ 1,538,973,000
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impaired Loans Valuation Allowance	332,000
Discount on appraisal value of foreclosed real estate, minimum (in hundredths)	9.00%
Discount on appraisal value of foreclosed real estate, maximum (in hundredths)	46.00%
Level 3 Assets Measured at Fair Value on a Recurring Basis [Abstract]
Beginning balance			42,051,000
Total gains (losses) included in earnings			(35,000)	[1],[2]
Total gains included in other comprehensive income			6,523,000	[3]
Principal reductions			(367,000)
Commitments to originate real estate loans held for sale, net			58,000
Ending balance			48,230,000
Financial liabilities:
Borrowings	1,004,813,000
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Pooled Trust Preferred Securities, Valuation Techniques	Consensus pricing
Impaired Loans, Valuation Techniques	Appraisals
Other Real Estate Owned, Valuation Techniques	Appraisals
Mortgage Servicing Rights, Valuation Techniques	Discounted cash flow
Pooled Trust Preferred Securities [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Total	47,385,000
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	47,385,000
Significant Unobservable Inputs, Inputs Description	Weighting of prices
Significant Unobservable Input Range, Minimum (in hundredths)	56.50%
Significant Unobservable Input Range, Maximum (in hundredths)	75.30%
Significant Unobservable Input Range, Weighted Average Fair Value (in hundredths)	69.10%
Impaired Loans [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Total	4,582,000
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	4,582,000
Significant Unobservable Inputs, Inputs Description	Estimated cost of disposal / market adjustment
Significant Unobservable Input Range, Minimum (in hundredths)	11.00%
Significant Unobservable Input Range, Maximum (in hundredths)	25.00%
Other Real Estate Owned [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Total	2,690,000
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	2,690,000
Significant Unobservable Inputs, Inputs Description	Estimated cost of disposal
Significant Unobservable Input Range, Minimum (in hundredths)	9.00%
Significant Unobservable Input Range, Maximum (in hundredths)	46.00%
Mortgage Servicing Rights [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Total	890,000
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	890,000
Significant Unobservable Inputs, Inputs Description	Weighted average constant prepayment rate
Constant Prepayment Input Range Minimum (in hundredths)	16.20%
Constant Prepayment Input Range Maximum (in hundredths)	29.30%
Constant Prepayment Input Range Weighted Average (in hundredths)	24.70%
Spread Over Market Curve Input Range Minimum (in hundredths)	2.98%
Spread Over Market Rate Input Range Maximum (in hundredths)	4.10%
Spread Over Market Rate Input Range Weighted Average (in hundredths)	3.68%
Adequate Compensation Input Range	$7/loan
Carrying [Member]
Financial assets:
Net loans	3,460,739,000				3,471,025,000
Financial liabilities:
Deposits	4,952,007,000				4,795,245,000
Borrowings	910,427,000				728,281,000
Subordinated debt held by unconsolidated subsidiary trusts	102,054,000				102,048,000
Fair Value Disclosure [Member]
Financial assets:
Net loans	3,468,883,000				3,491,729,000
Financial liabilities:
Deposits	4,964,875,000				4,810,856,000
Borrowings					828,018,000
Subordinated debt held by unconsolidated subsidiary trusts	75,196,000				73,211,000
Pooled Trust Preferred Securities [Member]
Level 3 Assets Measured at Fair Value on a Recurring Basis [Abstract]
Beginning balance	43,846,000		41,993,000
Total gains (losses) included in earnings	47,000	[1],[2]	23,000	[1],[2]
Total gains included in other comprehensive income	4,567,000	[3]	6,523,000	[3]
Principal reductions	(1,075,000)		(367,000)
Commitments to originate real estate loans held for sale, net	0		0
Ending balance	47,385,000		48,172,000
Commitments to Originate Real Estate Loans for Sale [Member]
Level 3 Assets Measured at Fair Value on a Recurring Basis [Abstract]
Beginning balance			58,000
Total gains (losses) included in earnings			(58,000)	[1],[2]
Total gains included in other comprehensive income			0	[3]
Principal reductions			0
Commitments to originate real estate loans held for sale, net			58,000
Ending balance			58,000
Fair Value, Measurements, Recurring [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	976,903,000				520,548,000
Obligations of state and political subdivisions	640,498,000				573,012,000
Government agency mortgage-backed securities	314,077,000				331,379,000
Pooled trust preferred securities	47,385,000				43,846,000
Corporate debt securities	22,789,000				22,855,000
Government agency collateralized mortgage obligations	43,310,000				46,943,000
Marketable equity securities	418,000				390,000
Total available-for-sale investment securities	2,045,380,000				1,538,973,000
Mortgage loans held for sale					532,000
Total					1,539,505,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	770,022,000				311,958,000
Obligations of state and political subdivisions	0				0
Government agency mortgage-backed securities	0				0
Pooled trust preferred securities	0				0
Corporate debt securities	0				0
Government agency collateralized mortgage obligations	0				0
Marketable equity securities	418,000				390,000
Total available-for-sale investment securities	770,440,000				312,348,000
Mortgage loans held for sale					0
Total					312,348,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	206,881,000				208,590,000
Obligations of state and political subdivisions	640,498,000				573,012,000
Government agency mortgage-backed securities	314,077,000				331,379,000
Pooled trust preferred securities	0				0
Corporate debt securities	22,789,000				22,855,000
Government agency collateralized mortgage obligations	43,310,000				46,943,000
Marketable equity securities	0				0
Total available-for-sale investment securities	1,227,555,000				1,182,779,000
Mortgage loans held for sale					532,000
Total					1,183,311,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	0				0
Obligations of state and political subdivisions	0				0
Government agency mortgage-backed securities	0				0
Pooled trust preferred securities	47,385,000				43,846,000
Corporate debt securities	0				0
Government agency collateralized mortgage obligations	0				0
Marketable equity securities	0				0
Total available-for-sale investment securities	47,385,000				43,846,000
Mortgage loans held for sale					0
Total					43,846,000
Fair Value, Measurements, Nonrecurring [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impaired loans	4,582,000				4,118,000
Other real estate owned	2,690,000				2,682,000
Mortgage servicing rights	890,000				1,747,000
Total	8,162,000				8,547,000
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	8,162,000				8,547,000
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impaired loans	0				0
Other real estate owned	0				0
Mortgage servicing rights	0				0
Total	0				0
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	0				0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impaired loans	0				0
Other real estate owned	0				0
Mortgage servicing rights	0				0
Total	0				0
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	0				0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impaired loans	4,582,000				4,118,000
Other real estate owned	2,690,000				2,682,000
Mortgage servicing rights	890,000				1,747,000
Total	8,162,000				8,547,000
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	$ 8,162,000				$ 8,547,000

[1] Amounts included in earnings associated with the commitments to originate real estate loans for sale are reported as a component of mortgage banking and other service fees.

[2] Amounts included in earnings associated with the pooled trust preferred securities relate to accretion of related discount and are reported in interest and dividends on taxable investments.

[3] Amounts included in other comprehensive income associated with the pooled trust preferred securities are relate to changes in unrealized loss and are reported as a component of unrealized gains on securities in the Statement of Comprehensive Income.