FAIR VALUE (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Available-for-sale investment securities:
Fair value	$ 1,706,304,000	$ 2,121,394,000
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Discount on appraisal value of foreclosed real estate, minimum (in hundredths)	4.00%
Discount on appraisal value of foreclosed real estate, maximum (in hundredths)	53.00%
Mortgage Servicing Rights, Valuation Allowance	400,000	400,000
Recurring [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	757,870,000	1,079,257,000
Obligations of state and political subdivisions	610,843,000	662,892,000
Government agency mortgage-backed securities	238,687,000	269,951,000
Pooled trust preferred securities	47,290,000	49,600,000
Government agency collateralized mortgage obligations	26,338,000	33,935,000
Corporate debt securities	24,798,000	25,357,000
Marketable equity securities	478,000	402,000
Fair value	1,706,304,000	2,121,394,000
Forward sales commitments	141,000
Commitments to originate real estate loans for sale	(19,000)
Mortgages loans held for sale	1,153,000
Total	1,707,579,000
Recurring [Member] | Level 1 [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	676,865,000	891,803,000
Obligations of state and political subdivisions	0	0
Government agency mortgage-backed securities	0	0
Pooled trust preferred securities	0	0
Government agency collateralized mortgage obligations	0	0
Corporate debt securities	0	0
Marketable equity securities	478,000	402,000
Fair value	677,343,000	892,205,000
Forward sales commitments	0
Commitments to originate real estate loans for sale	0
Mortgages loans held for sale	0
Total	677,343,000
Recurring [Member] | Level 2 [Member]
Available-for-sale investment securities:
U.S. Treasury and agency securities	81,005,000	187,454,000
Obligations of state and political subdivisions	610,843,000	662,892,000
Government agency mortgage-backed securities	238,687,000	269,951,000
Pooled trust preferred securities	0	0
Government agency collateralized mortgage obligations	26,338,000	33,935,000
Corporate debt securities	24,798,000	25,357,000
Marketable equity securities	0	0
Fair value	981,671,000	1,179,589,000
Forward sales commitments	141,000
Commitments to originate real estate loans for sale	0
Mortgages loans held for sale	1,153,000
Total	982,965,000
Mortgage loans held for sale, at principal value	1,167,000
Mortgage loans held for sale, Unrealized gains (losses)	14,000
Recurring [Member] | 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	47,290,000	49,600,000
Government agency collateralized mortgage obligations	0	0
Corporate debt securities	0	0
Marketable equity securities	0	0
Fair value	47,290,000	49,600,000
Forward sales commitments	0
Commitments to originate real estate loans for sale	(19,000)
Mortgages loans held for sale	0
Total	47,271,000
Nonrecurring [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impaired loan balance	1,990,000	1,186,000
Other real estate owned	5,066,000	4,788,000
Mortgage servicing rights	858,000	1,028,000
Total	7,914,000	7,002,000
Nonrecurring [Member] | Level 1 [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impaired loan balance	0	0
Other real estate owned	0	0
Mortgage servicing rights	0	0
Total	0	0
Nonrecurring [Member] | Level 2 [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impaired loan balance	0	0
Other real estate owned	0	0
Mortgage servicing rights	0	0
Total	0	0
Nonrecurring [Member] | Level 3 [Member]
Assets and Liabilities Measured on Nonrecurring Basis [Abstract]
Impaired loan balance	1,990,000	1,186,000
Other real estate owned	5,066,000	4,788,000
Mortgage servicing rights	858,000	1,028,000
Total	$ 7,914,000	$ 7,002,000