INVESTMENT SECURITIES (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	$ 1,465,705,000		$ 1,500,516,000
Gross Unrealized Gains	31,016,000		27,774,000
Gross Unrealized Losses	(19,248,000)		(33,545,000)
Carrying Value	1,477,473,000		1,494,745,000
Estimated fair value of available-for-sale securities pledged as collateral	291,900,000
Proceeds from investment securities previously held in portfolio and/or obtained in acquisition	142,041,000	12,810,000
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	560,004,000		691,944,000
Gross Unrealized Gains	16,204,000		18,012,000
Gross Unrealized Losses	(1,539,000)		(2,768,000)
Carrying Value	574,669,000		707,188,000
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	272,832,000		197,069,000
Gross Unrealized Gains	762,000		388,000
Gross Unrealized Losses	(3,957,000)		(4,584,000)
Carrying Value	269,637,000		192,873,000
Covered private label collateralized mortgage obligations
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	29,649,000		30,502,000
Gross Unrealized Gains	8,032,000		7,552,000
Gross Unrealized Losses	(87,000)		(150,000)
Carrying Value	37,594,000		37,904,000
Municipal securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	455,437,000		459,182,000
Gross Unrealized Gains	5,599,000		1,749,000
Gross Unrealized Losses	(13,103,000)		(24,273,000)
Carrying Value	447,933,000		436,658,000
Corporate debt securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	84,210,000		84,119,000
Gross Unrealized Gains	308,000		71,000
Gross Unrealized Losses	(307,000)		(1,483,000)
Carrying Value	84,211,000		82,707,000
Proceeds from investment securities previously held in portfolio and/or obtained in acquisition		12,400,000
Gross realized gain		409,000
Government-sponsored enterprise debt securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	36,180,000		10,046,000
Gross Unrealized Gains	74,000
Gross Unrealized Losses	(200,000)		(174,000)
Carrying Value	36,054,000		9,872,000
Proceeds from investment securities previously held in portfolio and/or obtained in acquisition	137,300,000
Gross realized gain	4,800,000
Other securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	27,393,000		27,654,000
Gross Unrealized Gains	37,000		2,000
Gross Unrealized Losses	(55,000)		(113,000)
Carrying Value	$ 27,375,000		$ 27,543,000