ALLOWANCE FOR CREDIT LOSSES (1) (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	$ 137,791,000	$ 156,728,000
Allowance for impaired loans and leases	11,658,000	10,541,000
Allowance for all other loans and leases	150,943,000	153,925,000
Total allowance	162,601,000	164,466,000	181,777,000	195,118,000
Evaluated for impairment threshold	500,000
Construction, acquisition and development [Member]
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	45,816,000	61,335,000
Allowance for impaired loans and leases	5,864,000	4,350,000
Commercial and industrial segment [Member]
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	3,459,000	4,845,000
Allowance for impaired loans and leases	763,000	1,241,000
Allowance for all other loans and leases	22,292,000	22,045,000
Total allowance	23,055,000	23,286,000	20,982,000	20,724,000
Real estate segment [Member] | Consumer mortgages [Member]
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	16,480,000	15,107,000
Allowance for impaired loans and leases	1,962,000	1,103,000
Allowance for all other loans and leases	33,696,000	34,863,000
Total allowance	35,658,000	35,966,000	36,548,000	36,529,000
Real estate segment [Member] | Home equity [Member]
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	2,037,000	1,380,000
Allowance for impaired loans and leases	32,000	111,000
Allowance for all other loans and leases	6,052,000	5,894,000
Total allowance	6,084,000	6,005,000	8,228,000	8,630,000
Real estate segment [Member] | Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	4,844,000	5,382,000
Allowance for impaired loans and leases	215,000	92,000
Allowance for all other loans and leases	3,505,000	3,209,000
Total allowance	3,720,000	3,301,000	3,386,000	3,921,000
Real estate segment [Member] | Commercial and industrial-owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	14,218,000	16,720,000
Allowance for impaired loans and leases	1,361,000	864,000
Allowance for all other loans and leases	19,022,000	19,314,000
Total allowance	20,383,000	20,178,000	20,642,000	21,929,000
Real estate segment [Member] | Construction, acquisition and development [Member]
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	45,816,000	61,335,000
Allowance for impaired loans and leases	5,864,000	4,350,000
Allowance for all other loans and leases	17,918,000	17,555,000
Total allowance	23,782,000	21,905,000	35,461,000	45,562,000
Real estate segment [Member] | Commercial real estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	49,703,000	50,413,000
Allowance for impaired loans and leases	1,461,000	2,720,000
Allowance for all other loans and leases	34,514,000	37,361,000
Total allowance	35,975,000	40,081,000	39,382,000	39,444,000
Credit cards segment [Member]
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	0	0
Allowance for impaired loans and leases	0	0
Allowance for all other loans and leases	3,399,000	3,611,000
Total allowance	3,399,000	3,611,000	3,141,000	4,021,000
All other [Member]
Financing Receivable, Impaired [Line Items]
Recorded balance of impaired loans	1,234,000	1,546,000
Allowance for impaired loans and leases	0	60,000
Allowance for all other loans and leases	10,545,000	10,073,000
Total allowance	$ 10,545,000	$ 10,133,000	$ 14,007,000	$ 14,358,000