INVESTMENT SECURITIES (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	$ 1,288,220	$ 1,287,042
Gross Unrealized Gains	69,490	41,789
Gross Unrealized Losses	(499)	(2,473)
Carrying Value	1,357,211	1,326,358
Government agency and government-sponsored enterprise pass through securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	901,955	1,011,222
Gross Unrealized Gains	43,777	31,350
Gross Unrealized Losses	(151)	(65)
Carrying Value	945,581	1,042,507
Government agency and government-sponsored enterprise collateralized mortgage obligations
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	89,320	80,353
Gross Unrealized Gains	2,128	1,710
Gross Unrealized Losses	(173)	(36)
Carrying Value	91,275	82,027
Covered private label collateralized mortgage obligations
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	37,116	41,426
Gross Unrealized Gains	8,932	5,878
Gross Unrealized Losses	(161)	(2,155)
Carrying Value	45,887	45,149
Municipal securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	236,385	124,079
Gross Unrealized Gains	10,909	2,774
Gross Unrealized Losses	(14)	(56)
Carrying Value	247,280	126,797
Corporate debt securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	17,049	25,077
Gross Unrealized Gains	206	77
Gross Unrealized Losses		(26)
Carrying Value	17,255	25,128
Other securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	6,395	4,885
Gross Unrealized Gains	3,538
Gross Unrealized Losses		(135)
Carrying Value	9,933	4,750
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	$ 975,700