SECURITIES (Details) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,629,274,000		$ 2,365,962,000
Gross Unrealized Gains	39,065,000		68,644,000
Gross Unrealized Losses	23,399,000		574,000
Estimated Fair Value	2,644,939,000	2,462,831,000	2,434,032,000	[1]
Gross gains recognized on available-for-sale securities	36,000	271,000
Gross losses recognized on available-for-sale securities	14,000	20,000
Equity securities, considered maturity	10 years
Available-for-sale securities, amortized cost, by contractual maturity [Abstract]
Maturing in one year or less	526,299,000
Maturing after one year through five years	1,188,888,000
Maturing after five years through ten years	450,391,000
Maturing after ten years	463,696,000
Total	2,629,274,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Maturing in one year or less	530,052,000
Maturing after one year through five years	1,193,864,000
Maturing after five years through ten years	444,938,000
Maturing after ten years	476,085,000
Estimated Fair Value	2,644,939,000	2,462,831,000	2,434,032,000	[1]
Available-for-sale securities, weighted average yield, by contractual maturity [Abstract]
Maturing in one year or less (in hundredths)	1.68%
Maturing after one year through five years (in hundredths)	1.34%
Maturing after five years through ten years (in hundredths)	3.39%
Maturing after ten years (in hundredths)	4.11%
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	783,655,000		138,820,000
Less Than 12 Months Unrealized Losses	23,216,000		417,000
12 Months or Longer Fair Value	6,079,000		3,152,000
12 Months or Longer Unrealized Losses	183,000		157,000
Total Fair Value Available-for-sale Securities	789,734,000		141,972,000
Total Unrealized Losses Available-for-sale Securities	23,399,000		574,000
US Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,575,837,000		1,380,979,000
Gross Unrealized Gains	13,082,000		21,081,000
Gross Unrealized Losses	7,349,000		64,000
Estimated Fair Value	1,581,570,000		1,401,996,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	1,581,570,000		1,401,996,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	460,267,000		47,395,000
Less Than 12 Months Unrealized Losses	7,349,000		64,000
Total Fair Value Available-for-sale Securities	460,267,000		47,395,000
Total Unrealized Losses Available-for-sale Securities	7,349,000		64,000
Government Agency Issued Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	288,345,000		358,677,000
Gross Unrealized Gains	5,584,000		8,457,000
Gross Unrealized Losses	1,342,000		259,000
Estimated Fair Value	292,586,000		366,875,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	292,586,000		366,875,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	52,219,000		55,939,000
Less Than 12 Months Unrealized Losses	1,195,000		145,000
12 Months or Longer Fair Value	5,534,000		2,839,000
12 Months or Longer Unrealized Losses	147,000		114,000
Total Fair Value Available-for-sale Securities	57,753,000		58,778,000
Total Unrealized Losses Available-for-sale Securities	1,342,000		259,000
Government Agency Issued Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	237,961,000		87,314,000
Gross Unrealized Gains	2,153,000		4,266,000
Gross Unrealized Losses	12,733,000		135,000
Estimated Fair Value	227,381,000		91,445,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	227,381,000		91,445,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	184,220,000		26,239,000
Less Than 12 Months Unrealized Losses	12,733,000		135,000
Total Fair Value Available-for-sale Securities	184,220,000		26,239,000
Total Unrealized Losses Available-for-sale Securities	12,733,000		135,000
Obligations Of States And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	520,067,000		531,940,000
Gross Unrealized Gains	17,245,000		34,049,000
Gross Unrealized Losses	1,975,000		116,000
Estimated Fair Value	535,337,000		565,873,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	535,337,000		565,873,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	86,949,000		9,247,000
Less Than 12 Months Unrealized Losses	1,939,000		73,000
12 Months or Longer Fair Value	545,000		313,000
12 Months or Longer Unrealized Losses	36,000		43,000
Total Fair Value Available-for-sale Securities	87,494,000		9,560,000
Total Unrealized Losses Available-for-sale Securities	1,975,000		116,000
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,064,000		7,052,000
Gross Unrealized Gains	1,001,000		791,000
Estimated Fair Value	8,065,000		7,843,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	8,065,000		7,843,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value
Less Than 12 Months Unrealized Losses
12 Months or Longer Fair Value
12 Months or Longer Unrealized Losses
Total Fair Value Available-for-sale Securities
Total Unrealized Losses Available-for-sale Securities

[1] Derived from audited financial statements.See accompanying notes to consolidated financial statements.