ALLOWANCE FOR CREDIT LOSSES (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of period	$ 164,466	$ 195,118	$ 195,118
Provision for credit losses	4,000	10,000	28,000
Recoveries	3,872	5,485	30,746
Loans and leases charged off	(9,737)	(28,826)	(89,398)
Balance at end of year	162,601	181,777	164,466
Commercial and industrial segment [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of period	23,286	20,724	20,724
Provision for credit losses	1,118	2,988	7,828
Recoveries	589	1,542	7,096
Loans and leases charged off	(1,938)	(4,272)	(12,362)
Balance at end of year	23,055	20,982	23,286
Real estate segment [Member] | Consumer mortgages [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of period	35,966	36,529	36,529
Provision for credit losses	198	3,912	10,723
Recoveries	1,108	323	1,836
Loans and leases charged off	(1,614)	(4,216)	(13,122)
Balance at end of year	35,658	36,548	35,966
Real estate segment [Member] | Home equity [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of period	6,005	8,630	8,630
Provision for credit losses	421	134	(400)
Recoveries	260	315	496
Loans and leases charged off	(602)	(851)	(2,721)
Balance at end of year	6,084	8,228	6,005
Real estate segment [Member] | Agricultural [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of period	3,301	3,921	3,921
Provision for credit losses	408	(449)	494
Recoveries	13	10	126
Loans and leases charged off	(2)	(96)	(1,240)
Balance at end of year	3,720	3,386	3,301
Real estate segment [Member] | Commercial and industrial-owner occupied [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of period	20,178	21,929	21,929
Provision for credit losses	251	2,230	4,568
Recoveries	254	351	2,696
Loans and leases charged off	(300)	(3,868)	(9,015)
Balance at end of year	20,383	20,642	20,178
Real estate segment [Member] | Construction, acquisition and development [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of period	21,905	45,562	45,562
Provision for credit losses	2,189	(862)	1,021
Recoveries	886	2,155	8,407
Loans and leases charged off	(1,198)	(11,394)	(33,085)
Balance at end of year	23,782	35,461	21,905
Real estate segment [Member] | Commercial real estate [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of period	40,081	39,444	39,444
Provision for credit losses	(1,304)	2,364	4,827
Recoveries	339	383	8,538
Loans and leases charged off	(3,141)	(2,809)	(12,728)
Balance at end of year	35,975	39,382	40,081
Credit cards segment [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of period	3,611	4,021	4,021
Provision for credit losses	90	(436)	1,284
Recoveries	148	118	527
Loans and leases charged off	(450)	(562)	(2,221)
Balance at end of year	3,399	3,141	3,611
All other [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of period	10,133	14,358	14,358
Provision for credit losses	629	119	(2,345)
Recoveries	275	288	1,024
Loans and leases charged off	(492)	(758)	(2,904)
Balance at end of year	$ 10,545	$ 14,007	$ 10,133