ALLOWANCE FOR CREDIT LOSSES (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year	$ 195,118	$ 196,913	$ 196,913
Loans and leases charged off	(28,826)	(53,750)	(142,055)
Recoveries	5,485	1,691	10,179
Provision charged to expense	10,000	53,479	130,081
Balance at end of year	181,777	198,333	195,118
Consumer mortgages [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year		35,540	35,540
Loans and leases charged off		(3,260)
Recoveries		143
Provision charged to expense		1,189
Balance at end of year		33,612
Home equity [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year		7,305	7,305
Loans and leases charged off		(1,082)
Recoveries		45
Provision charged to expense		1,424
Balance at end of year		7,692
Agricultural [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year		4,997	4,997
Loans and leases charged off		(592)
Recoveries		2
Provision charged to expense		40
Balance at end of year		4,447
Commercial and industrial-owner occupied [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year		20,403	20,403
Loans and leases charged off		(1,716)
Recoveries		173
Provision charged to expense		11,064
Balance at end of year		29,924
Construction, acquisition and development [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year		59,048	59,048
Loans and leases charged off		(32,343)
Recoveries		564
Provision charged to expense		26,959
Balance at end of year		54,228
Commercial [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year		33,439	33,439
Loans and leases charged off		(4,514)
Recoveries		13
Provision charged to expense		4,547
Balance at end of year		33,485
Commercial and industrial segment [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year	20,724	22,479	22,479
Loans and leases charged off	(4,272)	(8,809)	(17,337)
Recoveries	1,542	184	1,567
Provision charged to expense	2,988	6,525	14,015
Balance at end of year	20,982	20,379	20,724
Real estate segment [Member] | Consumer mortgages [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year	36,529	35,540	35,540
Loans and leases charged off	(4,216)		(10,186)
Recoveries	323		1,111
Provision charged to expense	3,912		10,064
Balance at end of year	36,548		36,529
Real estate segment [Member] | Home equity [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year	8,630	7,305	7,305
Loans and leases charged off	(851)		(5,852)
Recoveries	315		185
Provision charged to expense	134		6,992
Balance at end of year	8,228		8,630
Real estate segment [Member] | Agricultural [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year	3,921	4,997	4,997
Loans and leases charged off	(96)		(3,420)
Recoveries	10		123
Provision charged to expense	(449)		2,221
Balance at end of year	3,386		3,921
Real estate segment [Member] | Commercial and industrial-owner occupied [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year	21,929	20,403	20,403
Loans and leases charged off	(3,868)		(10,302)
Recoveries	351		393
Provision charged to expense	2,230		11,435
Balance at end of year	20,642		21,929
Real estate segment [Member] | Construction, acquisition and development [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year	45,562	59,048	59,048
Loans and leases charged off	(11,394)		(67,362)
Recoveries	2,155		3,951
Provision charged to expense	(862)		49,925
Balance at end of year	35,461		45,562
Real estate segment [Member] | Commercial [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year	39,444	33,439	33,439
Loans and leases charged off	(2,809)		(17,436)
Recoveries	383		1,045
Provision charged to expense	2,364		22,396
Balance at end of year	39,382		39,444
Credit cards segment [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year	4,021	4,126	4,126
Loans and leases charged off	(562)	(881)	(3,072)
Recoveries	118	255	803
Provision charged to expense	(436)	(54)	2,164
Balance at end of year	3,141	3,446	4,021
All other receivables [Member]
Changes in the allowance for credit losses [Roll Forward]
Balance at beginning of year	14,358	9,576	9,576
Loans and leases charged off	(758)	(553)	(7,088)
Recoveries	288	312	1,001
Provision charged to expense	119	1,785	10,869
Balance at end of year	$ 14,007	$ 11,120	$ 14,358