INVESTMENT SECURITIES (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	$ 1,295,676,000	$ 1,287,042,000
Gross Unrealized Gains	57,051,000	41,789,000
Gross Unrealized Losses	(1,026,000)	(2,473,000)
Carrying Value	1,351,701,000	1,326,358,000
Amortized Cost
Due in one year or less	44,886,000
Due after one year through five years	4,201,000
Due after five years through ten years	32,933,000
Due after ten years	1,213,656,000
Total securities available-for-sale	1,295,676,000	1,287,042,000
Carrying Value
Due in one year or less	48,219,000
Due after one year through five years	4,340,000
Due after five years through ten years	34,744,000
Due after ten years	1,264,398,000
Carrying Value	1,351,701,000	1,326,358,000
Estimated fair value of available-for-sale securities pledged as collateral	79,800,000
Government and government-sponsored entity pass through securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	949,984,000	1,011,222,000
Gross Unrealized Gains	39,096,000	31,350,000
Gross Unrealized Losses	(90,000)	(65,000)
Carrying Value	988,990,000	1,042,507,000
Amortized Cost
Total securities available-for-sale	949,984,000	1,011,222,000
Carrying Value
Carrying Value	988,990,000	1,042,507,000
Government and government-sponsored entity collateralized mortgage obligations
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	93,668,000	80,353,000
Gross Unrealized Gains	1,977,000	1,710,000
Gross Unrealized Losses	(40,000)	(36,000)
Carrying Value	95,605,000	82,027,000
Amortized Cost
Total securities available-for-sale	93,668,000	80,353,000
Carrying Value
Carrying Value	95,605,000	82,027,000
Covered private label collateralized mortgage obligations
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	37,944,000	41,426,000
Gross Unrealized Gains	6,609,000	5,878,000
Gross Unrealized Losses	(500,000)	(2,155,000)
Carrying Value	44,053,000	45,149,000
Amortized Cost
Total securities available-for-sale	37,944,000	41,426,000
Carrying Value
Carrying Value	44,053,000	45,149,000
Municipal securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	156,527,000	124,079,000
Gross Unrealized Gains	5,857,000	2,774,000
Gross Unrealized Losses	(192,000)	(56,000)
Carrying Value	162,192,000	126,797,000
Amortized Cost
Total securities available-for-sale	156,527,000	124,079,000
Carrying Value
Carrying Value	162,192,000	126,797,000
Corporate debt securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	51,162,000	25,077,000
Gross Unrealized Gains	61,000	77,000
Gross Unrealized Losses	(204,000)	(26,000)
Carrying Value	51,019,000	25,128,000
Amortized Cost
Total securities available-for-sale	51,162,000	25,077,000
Carrying Value
Carrying Value	51,019,000	25,128,000
Other securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	6,391,000	4,885,000
Gross Unrealized Gains	3,451,000
Gross Unrealized Losses		(135,000)
Carrying Value	9,842,000	4,750,000
Amortized Cost
Total securities available-for-sale	6,391,000	4,885,000
Carrying Value
Carrying Value	9,842,000	4,750,000
Debt securities and residential mortgage-backed securities issued by the Federal National Mortgage Association and federal Home Loan Mortgage Corporation
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Carrying Value	1,000,000,000
Carrying Value
Carrying Value	$ 1,000,000,000