INCOME TAXES (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current:
Federal	$ 18,875,000	$ 17,145,000	$ 13,090,000
State and other	830,000	375,000	776,000
Deferred:
Federal	9,051,000	10,674,000	7,633,000
State and other	2,981,000	2,191,000	1,566,000
Provision for income taxes	31,737,000	30,385,000	23,065,000
Components of net deferred tax liability [Abstract]
Allowance for loan losses	16,755,000	16,371,000
Employee benefits	6,748,000	6,718,000
Debt extinguishment	1,517,000	1,821,000
Other	2,292,000	2,169,000
Deferred tax asset	27,312,000	27,079,000
Investment securities	58,824,000	37,386,000
Intangible assets	16,648,000	9,448,000
Loan origination costs	6,069,000	5,041,000
Depreciation	5,138,000	5,779,000
Mortgage servicing rights	399,000	678,000
Pension	5,481,000	2,860,000
Prepaid FDIC insurance	0	3,079,000
Deferred tax liability	92,559,000	64,271,000
Net deferred tax liability	(65,247,000)	(37,192,000)
Effective tax rate reconciliation [Abstract]
Federal statutory income tax rate (in hundredths)	35.00%	35.00%	35.00%
Increase (reduction) in taxes resulting from:
Tax-exempt interest (in hundredths)	(7.10%)	(7.10%)	(8.30%)
State income taxes, net of federal benefit (in hundredths)	2.30%	1.60%	1.80%
Other (in hundredths)	(1.00%)	(0.10%)	(1.80%)
Effective income tax rate (in hundredths)	29.20%	29.40%	26.70%
Unrecognized tax benefits [Roll forward]
Unrecognized tax benefits at beginning of year	133,000	98,000	708,000
Changes related to:
Positions taken during the current year	35,000	35,000	35,000
Settlements with taxing authorities	(98,000)	0	(408,000)
Lapse of statutes of limitation	0	0	(237,000)
Unrecognized tax benefits at end of year	70,000	133,000	98,000
Unrecognized tax benefits that would impact effective tax rate, if recognized	$ 100,000