INVESTMENT SECURITIES (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	$ 1,500,516,000	$ 1,298,661,000
Gross Unrealized Gains	27,774,000	59,464,000
Gross Unrealized Losses	(33,545,000)	(2,740,000)
Carrying Value	1,494,745,000	1,355,385,000
Market purchases of investment securities available-for-sale by utilizing excess liquidity	550,211,000	485,860,000	658,310,000
Proceeds from investment securities previously held in portfolio and/or obtained in acquisition	22,415,000	90,745,000
Estimated fair value of available-for-sale securities pledged as collateral	208,300,000	157,300,000
American Perspective Bank
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Investment securities obtained in acquisition	48,900,000
Proceeds from investment securities previously held in portfolio and/or obtained in acquisition	45,600,000
Gain (loss) on sale of securities	0
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	691,944,000	774,677,000
Gross Unrealized Gains	18,012,000	33,618,000
Gross Unrealized Losses	(2,768,000)	(453,000)
Carrying Value	707,188,000	807,842,000
Proceeds from investment securities previously held in portfolio and/or obtained in acquisition		43,900,000
Gross realized gain		1,200,000
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	197,069,000	99,956,000
Gross Unrealized Gains	388,000	1,870,000
Gross Unrealized Losses	(4,584,000)	(132,000)
Carrying Value	192,873,000	101,694,000
Covered private label collateralized mortgage obligations
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	30,502,000	36,078,000
Gross Unrealized Gains	7,552,000	8,729,000
Gross Unrealized Losses	(150,000)	(123,000)
Carrying Value	37,904,000	44,684,000
Municipal securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	459,182,000	339,547,000
Gross Unrealized Gains	1,749,000	10,445,000
Gross Unrealized Losses	(24,273,000)	(1,951,000)
Carrying Value	436,658,000	348,041,000
Corporate debt securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	84,119,000	42,014,000
Gross Unrealized Gains	71,000	432,000
Gross Unrealized Losses	(1,483,000)	(81,000)
Carrying Value	82,707,000	42,365,000
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	10,046,000
Gross Unrealized Losses	(174,000)
Carrying Value	9,872,000
Other securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Amortized Cost	27,654,000	6,389,000
Gross Unrealized Gains	2,000	4,370,000
Gross Unrealized Losses	(113,000)
Carrying Value	27,543,000	10,759,000
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	740,400,000
Collateralized loan obligation securities
Amortized cost, gross unrealized gains and losses and estimated fair values of securities available-for-sale
Proceeds from investment securities previously held in portfolio and/or obtained in acquisition	10,000,000
Gross realized loss	$ 272,000