INVESTMENT SECURITIES (Details 2) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Amortized Cost
Due in one year or less	$ 3,774,000			$ 3,774,000
Due after one year through five years	24,449,000			24,449,000
Due after five years through ten years	124,905,000			124,905,000
Due after ten years	1,358,455,000			1,358,455,000
Total securities available-for-sale	1,511,583,000			1,511,583,000		1,298,661,000
Carrying Value
Due in one year or less	3,775,000			3,775,000
Due after one year through five years	24,707,000			24,707,000
Due after five years through ten years	124,317,000			124,317,000
Due after ten years	1,359,348,000			1,359,348,000
Carrying Value	1,512,147,000			1,512,147,000		1,355,385,000
Estimated fair value of available-for-sale securities pledged as collateral	201,900,000			201,900,000
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	683,669,000			683,669,000		192,738,000
Less Than 12 Months, Gross Unrealized Losses	(30,079,000)			(30,079,000)		(2,616,000)
12 months or Longer, Carrying Value	5,289,000			5,289,000		1,752,000
12 months or Longer, Gross Unrealized Losses	(135,000)			(135,000)		(124,000)
Total, Carrying Value	688,958,000			688,958,000		194,490,000
Total, Gross Unrealized Losses	(30,214,000)			(30,214,000)		(2,740,000)
Interest income on investment securities
Taxable interest	6,028,000	5,388,000	6,832,000	16,979,000	23,716,000
Nontaxable interest	3,302,000	2,716,000	1,458,000	8,443,000	3,572,000
Dividend income	541,000	310,000	56,000	1,079,000	196,000
Total interest income on investment securities	9,871,000	8,414,000	8,346,000	26,501,000	27,484,000
FHLB Stock
Investment in Federal Home Loan Bank stock carried at cost	34,095,000			34,095,000		37,126,000
Decrease in FHLB stock	5,000,000
Government agency and government-sponsored enterprise pass through securities
Amortized Cost
Total securities available-for-sale	695,768,000			695,768,000		774,677,000
Carrying Value
Carrying Value	713,962,000			713,962,000		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	124,088,000			124,088,000		67,299,000
Less Than 12 Months, Gross Unrealized Losses	(1,658,000)			(1,658,000)		(452,000)
12 months or Longer, Carrying Value	43,000			43,000		60,000
12 months or Longer, Gross Unrealized Losses	(1,000)			(1,000)		(1,000)
Total, Carrying Value	124,131,000			124,131,000		67,359,000
Total, Gross Unrealized Losses	(1,659,000)			(1,659,000)		(453,000)
Government agency and government-sponsored enterprise collateralized mortgage obligations
Amortized Cost
Total securities available-for-sale	201,531,000			201,531,000		99,956,000
Carrying Value
Carrying Value	199,360,000			199,360,000		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	139,846,000			139,846,000		18,317,000
Less Than 12 Months, Gross Unrealized Losses	(2,856,000)			(2,856,000)		(132,000)
12 months or Longer, Carrying Value	4,610,000			4,610,000
12 months or Longer, Gross Unrealized Losses	(45,000)			(45,000)
Total, Carrying Value	144,456,000			144,456,000		18,317,000
Total, Gross Unrealized Losses	(2,901,000)			(2,901,000)		(132,000)
Covered private label collateralized mortgage obligations
Amortized Cost
Total securities available-for-sale	31,503,000			31,503,000		36,078,000
Carrying Value
Carrying Value	39,378,000			39,378,000		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	543,000			543,000
Less Than 12 Months, Gross Unrealized Losses	(19,000)			(19,000)
12 months or Longer, Carrying Value	636,000			636,000		1,692,000
12 months or Longer, Gross Unrealized Losses	(89,000)			(89,000)		(123,000)
Total, Carrying Value	1,179,000			1,179,000		1,692,000
Total, Gross Unrealized Losses	(108,000)			(108,000)		(123,000)
Municipal securities
Amortized Cost
Total securities available-for-sale	460,754,000			460,754,000		339,547,000
Carrying Value
Carrying Value	439,635,000			439,635,000		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	323,419,000			323,419,000		90,303,000
Less Than 12 Months, Gross Unrealized Losses	(23,269,000)			(23,269,000)		(1,951,000)
Total, Carrying Value	323,419,000			323,419,000		90,303,000
Total, Gross Unrealized Losses	(23,269,000)			(23,269,000)		(1,951,000)
Corporate debt securities
Amortized Cost
Total securities available-for-sale	84,028,000			84,028,000		42,014,000
Carrying Value
Carrying Value	82,106,000			82,106,000		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	61,831,000			61,831,000		16,819,000
Less Than 12 Months, Gross Unrealized Losses	(1,983,000)			(1,983,000)		(81,000)
Total, Carrying Value	61,831,000			61,831,000		16,819,000
Total, Gross Unrealized Losses	(1,983,000)			(1,983,000)		(81,000)
Other securities
Amortized Cost
Total securities available-for-sale	37,999,000			37,999,000		6,389,000
Carrying Value
Carrying Value	37,706,000			37,706,000		10,759,000
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	33,942,000			33,942,000
Less Than 12 Months, Gross Unrealized Losses	(294,000)			(294,000)
Total, Carrying Value	33,942,000			33,942,000
Total, Gross Unrealized Losses	$ (294,000)			$ (294,000)