INVESTMENT SECURITIES (Details) (USD $)	3 Months Ended		3 Months Ended								3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2012 Government agency and government-sponsored enterprise pass through securities	Mar. 31, 2013 Government agency and government-sponsored enterprise pass through securities	Mar. 31, 2013 Government agency and government-sponsored enterprise collateralized mortgage obligations	Dec. 31, 2012 Government agency and government-sponsored enterprise collateralized mortgage obligations	Mar. 31, 2013 Covered private label collateralized mortgage obligations	Dec. 31, 2012 Covered private label collateralized mortgage obligations	Mar. 31, 2013 Municipal securities	Dec. 31, 2012 Municipal securities	Mar. 31, 2013 Corporate debt securities	Dec. 31, 2012 Corporate debt securities	Mar. 31, 2013 Other securities	Dec. 31, 2012 Other securities	Mar. 31, 2013 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
Amortized Cost	$ 1,312,872,000	$ 1,298,661,000	$ 774,677,000	$ 751,011,000	$ 97,524,000	$ 99,956,000	$ 34,933,000	$ 36,078,000	$ 362,212,000	$ 339,547,000	$ 60,807,000	$ 42,014,000	$ 6,385,000	$ 6,389,000
Gross Unrealized Gains	55,111,000	59,464,000	33,618,000	30,808,000	1,742,000	1,870,000	8,974,000	8,729,000	7,926,000	10,445,000	416,000	432,000	5,245,000	4,370,000
Gross Unrealized Losses	(5,206,000)	(2,740,000)	(453,000)	(191,000)	(161,000)	(132,000)	(122,000)	(123,000)	(4,713,000)	(1,951,000)	(19,000)	(81,000)
Carrying Value	1,362,777,000	1,355,385,000	807,842,000	781,628,000	99,105,000	101,694,000	43,785,000	44,684,000	365,425,000	348,041,000	61,204,000	42,365,000	11,630,000	10,759,000	797,300,000
Proceeds from investment securities previously held in portfolio and/or obtained in acquisition	12,810,000		43,900,000								12,400,000
Gross realized gain			$ 1,200,000								$ 409,000