INVESTMENT SECURITIES (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Amortized Cost
Due in one year or less	$ 7,375,000
Due after one year through five years	3,940,000
Due after five years through ten years	51,365,000
Due after ten years	1,250,192,000
Total securities available-for-sale	1,312,872,000	1,298,661,000
Carrying Value
Due in one year or less	12,758,000
Due after one year through five years	4,117,000
Due after five years through ten years	53,467,000
Due after ten years	1,292,435,000
Carrying Value	1,362,777,000	1,355,385,000
Estimated fair value of available-for-sale securities pledged as collateral	157,500,000
Carrying values and gross unrealized losses on securities by length of time the securities were in an unrealized loss position
Less Than 12 Months, Carrying Value	254,130,000	192,738,000
Less Than 12 Months, Gross Unrealized Losses	(5,066,000)	(2,616,000)
12 months or Longer, Carrying Value	3,584,000	1,752,000
12 months or Longer, Gross Unrealized Losses	(140,000)	(124,000)
Total, Carrying Value	257,714,000	194,490,000
Total, Gross Unrealized Losses	(5,206,000)	(2,740,000)
Interest income on investment securities
Taxable interest	5,563,000	5,915,000	8,539,000
Nontaxable interest	2,425,000	1,987,000	980,000
Dividend income	228,000	271,000	61,000
Total interest income on investment securities	8,216,000	8,173,000	9,580,000
FHLB Stock
Investment in Federal Home Loan Bank stock carried at cost	33,400,000	37,126,000
Government agency and government-sponsored enterprise pass through securities
Amortized Cost
Total securities available-for-sale	751,011,000	774,677,000
Carrying Value
Carrying Value	781,628,000	807,842,000
Carrying values and gross unrealized losses on securities by length of time the securities were in an unrealized loss position
Less Than 12 Months, Carrying Value	47,483,000	67,299,000
Less Than 12 Months, Gross Unrealized Losses	(190,000)	(452,000)
12 months or Longer, Carrying Value	57,000	60,000
12 months or Longer, Gross Unrealized Losses	(1,000)	(1,000)
Total, Carrying Value	47,540,000	67,359,000
Total, Gross Unrealized Losses	(191,000)	(453,000)
Government agency and government-sponsored enterprise collateralized mortgage obligations
Amortized Cost
Total securities available-for-sale	97,524,000	99,956,000
Carrying Value
Carrying Value	99,105,000	101,694,000
Carrying values and gross unrealized losses on securities by length of time the securities were in an unrealized loss position
Less Than 12 Months, Carrying Value	16,967,000	18,317,000
Less Than 12 Months, Gross Unrealized Losses	(128,000)	(132,000)
12 months or Longer, Carrying Value	1,994,000
12 months or Longer, Gross Unrealized Losses	(33,000)
Total, Carrying Value	18,961,000	18,317,000
Total, Gross Unrealized Losses	(161,000)	(132,000)
Covered private label collateralized mortgage obligations
Amortized Cost
Total securities available-for-sale	34,933,000	36,078,000
Carrying Value
Carrying Value	43,785,000	44,684,000
Carrying values and gross unrealized losses on securities by length of time the securities were in an unrealized loss position
Less Than 12 Months, Carrying Value	465,000
Less Than 12 Months, Gross Unrealized Losses	(16,000)
12 months or Longer, Carrying Value	1,533,000	1,692,000
12 months or Longer, Gross Unrealized Losses	(106,000)	(123,000)
Total, Carrying Value	1,998,000	1,692,000
Total, Gross Unrealized Losses	(122,000)	(123,000)
Municipal securities
Amortized Cost
Total securities available-for-sale	362,212,000	339,547,000
Carrying Value
Carrying Value	365,425,000	348,041,000
Carrying values and gross unrealized losses on securities by length of time the securities were in an unrealized loss position
Less Than 12 Months, Carrying Value	184,175,000	90,303,000
Less Than 12 Months, Gross Unrealized Losses	(4,713,000)	(1,951,000)
Total, Carrying Value	184,175,000	90,303,000
Total, Gross Unrealized Losses	(4,713,000)	(1,951,000)
Corporate debt securities
Amortized Cost
Total securities available-for-sale	60,807,000	42,014,000
Carrying Value
Carrying Value	61,204,000	42,365,000
Carrying values and gross unrealized losses on securities by length of time the securities were in an unrealized loss position
Less Than 12 Months, Carrying Value	5,040,000	16,819,000
Less Than 12 Months, Gross Unrealized Losses	(19,000)	(81,000)
Total, Carrying Value	5,040,000	16,819,000
Total, Gross Unrealized Losses	$ (19,000)	$ (81,000)