INCOME TAXES (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Allocation of income taxes [Abstract]
Income tax expense (benefit)	$ 33,252,000	$ 4,475,000	$ (8,705,000)
Shareholders' equity for other comprehensive income	(3,943,000)	7,600,000	(3,763,000)
Shareholders' equity for stock option plans	32,000	(7,000)	(44,000)
Total	29,341,000	12,068,000	(12,512,000)
Current [Abstract]
Federal	34,316,000	5,643,000	8,865,000
State	3,389,000	5,400,000	(1,520,000)
Deferred [Abstract]
Federal	(4,964,000)	(1,626,000)	(13,848,000)
State	511,000	(4,942,000)	(2,202,000)
Total	33,252,000	4,475,000	(8,705,000)
Statutory federal income tax rate (in hundredths)	35.00%	35.00%	35.00%
Income tax reconciliation [Abstract]
Tax expense at statutory rates	41,141,000	14,715,000	4,983,000
Increase (decrease) in taxes resulting from [Abstract]
State income taxes, net of federal tax benefit	2,453,000	266,000	(2,419,000)
Tax-exempt interest revenue	(7,789,000)	(7,881,000)	(6,605,000)
Tax-exempt earnings on life insurance	(2,790,000)	(2,647,000)	(2,659,000)
Deductible dividends paid on 401(k) plan	(100,000)	(331,000)	(1,972,000)
Other, net	337,000	353,000	(33,000)
Total	33,252,000	4,475,000	(8,705,000)
Deferred tax assets [Abstract]
Loans, principally due to allowance for credit losses	62,206,000	73,911,000
Other real estate owned	13,027,000	10,429,000
Mark to market - securities	4,160,000	4,165,000
Accrued liabilities, principally due to compensation arrangements and vacation accruals	19,564,000	10,681,000
Other	217,000	312,000
Investments, principally due to interest income recognition	516,000	0
State tax credits (net of federal benefit)	428,000	1,040,000
Unrecognized pension expense	31,374,000	26,428,000
Total gross deferred tax assets	131,492,000	126,966,000
Less: valuation allowance	0	0
Deferred tax assets	131,492,000	126,966,000
Deferred tax liabilities [Abstract]
Lease transactions	34,532,000	37,509,000
Employment benefits	22,392,000	26,991,000
Premises and equipment, principally due to differences in depreciation	26,824,000	27,221,000
Mortgage servicing rights	14,313,000	11,405,000
Intangible assets	10,439,000	10,336,000
Investments, principally due to interest income recognition	0	147,000
Deferred loan points	2,650,000	2,656,000
Other assets, principally due to expense recognition	767,000	525,000
Unrealized net losses on available-for-sale securities	26,066,000	25,064,000
Total gross deferred tax liabilities	137,983,000	141,854,000
Net deferred tax liabilities	(6,491,000)	(14,888,000)
Deferred state tax asset	428,000
Activity in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefit, January 1	1,102,000	355,000	355,000
Gross increases - tax positions in prior period	199,000	873,000	0
Gross decreases - tax positions in prior period	0	(355,000)	0
Gross increases - tax positions in current period	270,000	229,000	0
Settlements	0	0	0
Lapse of statute of limitations	0	0	0
Unrecognized tax benefit, December 31	1,571,000	1,102,000	355,000
Tax benefits that, if recognized, would affect the effective tax rate	1,600,000	1,100,000	355,000
Interest related to unrecognized tax benefits	329,000	26,000	28,000
Liability for interest	$ 560,000	$ 231,000	$ 191,000