INCOME TAXES (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Allocation of income taxes [Abstract]
Income tax expense (benefit)	$ 37,551,000	$ 33,252,000	$ 4,475,000
Shareholders' equity for other comprehensive income	(13,249,000)	(3,943,000)	7,600,000
Shareholders' equity for stock option plans	(139,000)	32,000	(7,000)
Total	24,163,000	29,341,000	12,068,000
Current [Abstract]
Federal	32,729,000	34,316,000	5,643,000
State	1,570,000	3,389,000	5,400,000
Deferred [Abstract]
Federal	1,774,000	(4,964,000)	(1,626,000)
State	1,478,000	511,000	(4,942,000)
Total	37,551,000	33,252,000	4,475,000
Statutory federal income tax rate (in hundredths)	35.00%	35.00%	35.00%
Income tax reconciliation [Abstract]
Reversal of deferred tax asset	1,100,000
Tax expense at statutory rates	46,083,000	41,141,000	14,715,000
Increase (decrease) in taxes resulting from [Abstract]
State income taxes, net of federal tax benefit	1,926,000	2,453,000	266,000
Tax-exempt interest revenue	(7,423,000)	(7,789,000)	(7,881,000)
Tax-exempt earnings on life insurance	(2,889,000)	(2,790,000)	(2,647,000)
Deductible dividends paid on 401(k) plan	(187,000)	(100,000)	(331,000)
Other, net	41,000	337,000	353,000
Total	37,551,000	33,252,000	4,475,000
Deferred tax assets [Abstract]
Loans, principally due to allowance for credit losses	58,003,000	62,206,000
Other real estate owned	6,799,000	13,027,000
Mark to market - securities	4,164,000	4,160,000
Accrued liabilities, principally due to compensation arrangements and vacation accruals	13,085,000	15,897,000
Other	2,993,000	3,884,000
Investments, principally due to interest income recognition		516,000
State tax credits (net of federal benefit)		428,000
Unrecognized pension expense	20,997,000	31,374,000
Total gross deferred tax assets	106,041,000	131,492,000
Less: valuation allowance
Deferred tax assets	106,041,000	131,492,000
Deferred tax liabilities [Abstract]
Lease transactions	29,997,000	34,532,000
Employment benefits	12,483,000	22,392,000
Premises and equipment, principally due to differences in depreciation	23,488,000	26,824,000
Mortgage servicing rights	20,679,000	14,313,000
Intangible assets	10,654,000	10,439,000
Investments, principally due to interest income recognition	133,000
Deferred loan points	2,806,000	2,650,000
Other assets, principally due to expense recognition	1,033,000	767,000
Unrealized net losses on available-for-sale securities	2,289,000	26,066,000
Total gross deferred tax liabilities	103,562,000	137,983,000
Net deferred tax liabilities	2,479,000	(6,491,000)
Activity in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefit, January 1	1,571,000	1,102,000	355,000
Gross increases - tax positions in prior period		199,000	873,000
Gross decreases - tax positions in prior period	(1,571,000)		(355,000)
Gross increases - tax positions in current period		270,000	229,000
Settlements
Lapse of statute of limitations
Unrecognized tax benefit, December 31		1,571,000	1,102,000
Tax benefits that, if recognized, would affect the effective tax rate		1,600,000	1,100,000
Interest related to unrecognized tax benefits		329,000	26,000
Liability for interest	0	560,000	231,000
Tax benefit recorded as result of resolution of uncertain tax position	$ 1,600,000