AVAILABLE-FOR-SALE SECURITIES (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,365,962,000	$ 2,448,051,000
Gross Unrealized Gains	68,644,000	65,884,000
Gross Unrealized Losses	574,000	417,000
Estimated Fair Value	2,434,032,000	2,513,518,000
Carrying value of FHLB stock	6,800,000
Required investment in FHLB stock	6,600,000
Gross gains recognized on available-for-sale securities	480,000	12,400,000	4,500,000
Gross losses recognized on available-for-sale securities	38,000	327,000	2,100,000
Carrying value of available-for-sale securities pledged	1,700,000,000
Equity securities, considered maturity	10 years
Available-for-sale securities, amortized cost, by contractual maturity [Abstract]
Maturing in one year or less	450,236,000
Maturing after one year through five years	1,055,838,000
Maturing after five years through ten years	341,992,000
Maturing after ten years	517,896,000
Total	2,365,962,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Maturing in one year or less	453,843
Maturing after one year through five years	1,077,403,000
Maturing after five years through ten years	357,489,000
Maturing after ten years	545,297,000
Estimated Fair Value	2,434,032,000	2,513,518,000
Available-for-sale securities, weighted average yield, by contractual maturity [Abstract]
Maturing in one year or less (in hundredths)	1.77%
Maturing after one year through five years (in hundredths)	1.61%
Maturing after five years through ten years (in hundredths)	4.00%
Maturing after ten years (in hundredths)	4.25%
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	138,820,000	55,670,000
Less Than 12 Months Unrealized Losses	417,000	168,000
12 Months or Longer Fair Value	3,152,000	12,965,000
12 Months or Longer Unrealized Losses	157,000	249,000
Total Fair Value	141,972,000	68,635,000
Total Unrealized Losses	574,000	417,000
State of Mississippi [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying value of available-for-sale securities pledged	273,600,000
State of Arkansas [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying value of available-for-sale securities pledged	141,500,000
U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,380,979,000	1,471,920,000
Gross Unrealized Gains	21,081,000	29,347,000
Gross Unrealized Losses	64,000	24,000
Estimated Fair Value	1,401,996,000	1,501,243,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	1,401,996,000	1,501,243,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	47,395,000	34,850,000
Less Than 12 Months Unrealized Losses	64,000	24,000
12 Months or Longer Fair Value	0	0
12 Months or Longer Unrealized Losses	0	0
Total Fair Value	47,395,000	34,850,000
Total Unrealized Losses	64,000	24,000
Government Agency Issued Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	358,677,000	394,894,000
Gross Unrealized Gains	8,457,000	9,786,000
Gross Unrealized Losses	259,000	70,000
Estimated Fair Value	366,875,000	404,610,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	366,875,000	404,610,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	55,939,000	0
Less Than 12 Months Unrealized Losses	145,000	0
12 Months or Longer Fair Value	2,839,000	3,751,000
12 Months or Longer Unrealized Losses	114,000	70,000
Total Fair Value	58,778,000	3,751,000
Total Unrealized Losses	259,000	70,000
Government Agency Issued Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	87,314,000	31,161,000
Gross Unrealized Gains	4,266,000	3,438,000
Gross Unrealized Losses	135,000	0
Estimated Fair Value	91,445,000	34,599,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	91,445,000	34,599,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	26,239,000	0
Less Than 12 Months Unrealized Losses	135,000	0
12 Months or Longer Fair Value	0	0
12 Months or Longer Unrealized Losses	0	0
Total Fair Value	26,239,000	0
Total Unrealized Losses	135,000	0
Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	531,940,000	541,138,000
Gross Unrealized Gains	34,049,000	22,705,000
Gross Unrealized Losses	116,000	323,000
Estimated Fair Value	565,873,000	563,520,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	565,873,000	563,520,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	9,247,000	20,820,000
Less Than 12 Months Unrealized Losses	73,000	144,000
12 Months or Longer Fair Value	313,000	9,214,000
12 Months or Longer Unrealized Losses	43,000	179,000
Total Fair Value	9,560,000	30,034,000
Total Unrealized Losses	116,000	323,000
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,052,000	8,938,000
Gross Unrealized Gains	791,000	608,000
Gross Unrealized Losses	0	0
Estimated Fair Value	7,843,000	9,546,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	7,843,000	9,546,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	0	0
Less Than 12 Months Unrealized Losses	0	0
12 Months or Longer Fair Value	0	0
12 Months or Longer Unrealized Losses	0	0
Total Fair Value	0	0
Total Unrealized Losses	$ 0	$ 0