AVAILABLE-FOR-SALE SECURITIES (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,460,608,000	$ 2,365,962,000
Gross Unrealized Gains	27,987,000	68,644,000
Gross Unrealized Losses	21,606,000	574,000
Estimated Fair Value	2,466,989,000	2,434,032,000
Carrying value of FHLB stock	6,800,000
Required investment in FHLB stock	6,700,000
Gross gains recognized on available-for-sale securities	72,000	480,000	12,400,000
Gross losses recognized on available-for-sale securities	26,000	38,000	327,000
Carrying value of available-for-sale securities pledged	1,800,000,000
Available-for-sale securities, amortized cost, by contractual maturity [Abstract]
Maturing in one year or less	504,785,000
Maturing after one year through five years	1,091,317,000
Maturing after five years through ten years	160,222,000
Maturing after ten years	215,289,000
Mortgage-backed securities	488,995,000
Total	2,460,608,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Maturing in one year or less	507,800,000
Maturing after one year through five years	1,093,947,000
Maturing after five years through ten years	163,839,000
Maturing after ten years	220,257,000
Mortgage-backed securities	481,146,000
Estimated Fair Value	2,466,989,000	2,434,032,000
Available-for-sale securities, weighted average yield, by contractual maturity [Abstract]
Maturing in one year or less (in hundredths)	1.52%
Maturing after one year through five years (in hundredths)	1.30%
Maturing after five years through ten years (in hundredths)	5.71%
Maturing after ten years (in hundredths)	5.86%
Mortgage-backed securities (in hundredths)	2.15%
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	913,301,000	138,820,000
Less Than 12 Months Unrealized Losses	19,684,000	417,000
12 Months or Longer Fair Value	35,295,000	3,152,000
12 Months or Longer Unrealized Losses	1,922,000	157,000
Total Fair Value	948,596,000	141,972,000
Total Unrealized Losses	21,606,000	574,000
Mississippi [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying value of available-for-sale securities pledged	255,200,000
Arkansas [Member]
Schedule of Available-for-sale Securities [Line Items]
Carrying value of available-for-sale securities pledged	115,100,000
U.S. Agency Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,455,417,000	1,380,979,000
Gross Unrealized Gains	9,065,000	21,081,000
Gross Unrealized Losses	6,133,000	64,000
Estimated Fair Value	1,458,349,000	1,401,996,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	1,458,349,000	1,401,996,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	533,326,000	47,395,000
Less Than 12 Months Unrealized Losses	6,133,000	64,000
Total Fair Value	533,326,000	47,395,000
Total Unrealized Losses	6,133,000	64,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	249,682,000	358,677,000
Gross Unrealized Gains	3,118,000	8,457,000
Gross Unrealized Losses	2,566,000	259,000
Estimated Fair Value	250,234,000	366,875,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	250,234,000	366,875,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	106,179,000	55,939,000
Less Than 12 Months Unrealized Losses	2,418,000	145,000
12 Months or Longer Fair Value	4,407,000	2,839,000
12 Months or Longer Unrealized Losses	148,000	114,000
Total Fair Value	110,586,000	58,778,000
Total Unrealized Losses	2,566,000	259,000
Government Agency Issued Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	239,313,000	87,314,000
Gross Unrealized Gains	1,773,000	4,266,000
Gross Unrealized Losses	10,174,000	135,000
Estimated Fair Value	230,912,000	91,445,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	230,912,000	91,445,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	176,253,000	26,239,000
Less Than 12 Months Unrealized Losses	8,578,000	135,000
12 Months or Longer Fair Value	27,225,000
12 Months or Longer Unrealized Losses	1,596,000
Total Fair Value	203,478,000	26,239,000
Total Unrealized Losses	10,174,000	135,000
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	509,255,000	531,940,000
Gross Unrealized Gains	12,883,000	34,049,000
Gross Unrealized Losses	2,733,000	116,000
Estimated Fair Value	519,405,000	565,873,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	519,405,000	565,873,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	97,543,000	9,247,000
Less Than 12 Months Unrealized Losses	2,555,000	73,000
12 Months or Longer Fair Value	3,663,000	313,000
12 Months or Longer Unrealized Losses	178,000	43,000
Total Fair Value	101,206,000	9,560,000
Total Unrealized Losses	2,733,000	116,000
Other Available for Sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,941,000	7,052,000
Gross Unrealized Gains	1,148,000	791,000
Estimated Fair Value	8,089,000	7,843,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	$ 8,089,000	$ 7,843,000