SECURITIES (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,539,925,000		$ 2,365,962,000
Gross Unrealized Gains	34,463,000		68,644,000
Gross Unrealized Losses	20,232,000		574,000
Estimated Fair Value	2,554,156,000	2,483,606,000	2,434,032,000	[1]
Gross gains recognized on available-for-sale securities	43,000	329,000
Gross losses recognized on available-for-sale securities	26,000	39,000
Equity securities, considered maturity	10 years
Available-for-sale securities, amortized cost, by contractual maturity [Abstract]
Maturing in one year or less	518,661,000
Maturing after one year through five years	1,132,003,000
Maturing after five years through ten years	161,230,000
Maturing after ten years	224,379,000
Mortgage-backed securities	503,652,000
Total	2,539,925,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Maturing in one year or less	521,825,000
Maturing after one year through five years	1,138,516,000
Maturing after five years through ten years	165,642,000
Maturing after ten years	230,394,000
Mortgage-backed securities	497,779,000
Estimated Fair Value	2,554,156,000	2,483,606,000	2,434,032,000	[1]
Available-for-sale securities, weighted average yield, by contractual maturity [Abstract]
Maturing in one year or less (in hundredths)	1.62%
Maturing after one year through five years (in hundredths)	1.33%
Maturing after five years through ten years (in hundredths)	5.74%
Maturing after ten years (in hundredths)	5.92%
Mortgage-backed securities (in hundredths)	2.04%
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	764,904,000		138,820,000
Less Than 12 Months Unrealized Losses	19,832,000		417,000
12 Months or Longer Fair Value	16,128,000		3,152,000
12 Months or Longer Unrealized Losses	400,000		157,000
Total Fair Value Available-for-sale Securities	781,032,000		141,972,000
Total Unrealized Losses Available-for-sale Securities	20,232,000		574,000
US Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,512,554,000		1,380,979,000
Gross Unrealized Gains	11,921,000		21,081,000
Gross Unrealized Losses	5,016,000		64,000
Estimated Fair Value	1,519,459,000		1,401,996,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	1,519,459,000		1,401,996,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	396,667,000		47,395,000
Less Than 12 Months Unrealized Losses	5,016,000		64,000
Total Fair Value Available-for-sale Securities	396,667,000		47,395,000
Total Unrealized Losses Available-for-sale Securities	5,016,000		64,000
Government Agency Issued Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	265,163,000		358,677,000
Gross Unrealized Gains	4,673,000		8,457,000
Gross Unrealized Losses	1,469,000		259,000
Estimated Fair Value	268,367,000		366,875,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	268,367,000		366,875,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	74,939,000		55,939,000
Less Than 12 Months Unrealized Losses	1,319,000		145,000
12 Months or Longer Fair Value	4,749,000		2,839,000
12 Months or Longer Unrealized Losses	150,000		114,000
Total Fair Value Available-for-sale Securities	79,688,000		58,778,000
Total Unrealized Losses Available-for-sale Securities	1,469,000		259,000
Government Agency Issued Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	238,489,000		87,314,000
Gross Unrealized Gains	2,026,000		4,266,000
Gross Unrealized Losses	11,103,000		135,000
Estimated Fair Value	229,412,000		91,445,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	229,412,000		91,445,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	190,975,000		26,239,000
Less Than 12 Months Unrealized Losses	10,900,000		135,000
12 Months or Longer Fair Value	10,606,000
12 Months or Longer Unrealized Losses	203,000
Total Fair Value Available-for-sale Securities	201,581,000		26,239,000
Total Unrealized Losses Available-for-sale Securities	11,103,000		135,000
Obligations Of States And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	516,784,000		531,940,000
Gross Unrealized Gains	14,749,000		34,049,000
Gross Unrealized Losses	2,644,000		116,000
Estimated Fair Value	528,889,000		565,873,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	528,889,000		565,873,000
Available-for-sale securities with continuous unrealized loss positions [Abstract]
Less Than 12 Months Fair Value	102,323,000		9,247,000
Less Than 12 Months Unrealized Losses	2,597,000		73,000
12 Months or Longer Fair Value	773,000		313,000
12 Months or Longer Unrealized Losses	47,000		43,000
Total Fair Value Available-for-sale Securities	103,096,000		9,560,000
Total Unrealized Losses Available-for-sale Securities	2,644,000		116,000
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,935,000		7,052,000
Gross Unrealized Gains	1,094,000		791,000
Estimated Fair Value	8,029,000		7,843,000
Available-for-sale securities, estimated fair value, by contractual maturity [Abstract]
Estimated Fair Value	8,029,000		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.