INVESTMENT SECURITIES (Details 4) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	$ 541,980	$ 620,165
Continuous unrealized loss position less than 12 months, unrealized losses	(6,599)	(6,989)
Continuous unrealized loss position 12 months or more, fair value	118,665	195,271
Continuous unrealized loss position 12 months or more, unrealized losses	(11,402)	(19,739)
Continuous unrealized loss position total, fair value	660,645	815,436
Continuous unrealized loss position total, unrealized losses	(18,001)	(26,728)
U.S. Treasury securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	52,587	95,232
Continuous unrealized loss position less than 12 months, unrealized losses	(31)	(71)
Continuous unrealized loss position total, fair value	52,587	95,232
Continuous unrealized loss position total, unrealized losses	(31)	(71)
U.S. Government agency and U.S. Government sponsored enterprise debt securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	24,874	24,912
Continuous unrealized loss position less than 12 months, unrealized losses	(120)	(82)
Continuous unrealized loss position total, fair value	24,874	24,912
Continuous unrealized loss position total, unrealized losses	(120)	(82)
U.S. Government agency and U.S. Government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	44,066	10,013
Continuous unrealized loss position less than 12 months, unrealized losses	(411)	(36)
Continuous unrealized loss position total, fair value	44,066	10,013
Continuous unrealized loss position total, unrealized losses	(411)	(36)
U.S. Government agency and U.S. Government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	203,984	215,826
Continuous unrealized loss position less than 12 months, unrealized losses	(1,301)	(678)
Continuous unrealized loss position total, fair value	203,984	215,826
Continuous unrealized loss position total, unrealized losses	(1,301)	(678)
Municipal securities
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	120,187	48,363
Continuous unrealized loss position less than 12 months, unrealized losses	(2,639)	(731)
Continuous unrealized loss position total, fair value	120,187	48,363
Continuous unrealized loss position total, unrealized losses	(2,639)	(731)
Corporate debt securities | Investment grade
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	94,204	225,819
Continuous unrealized loss position less than 12 months, unrealized losses	(2,044)	(5,391)
Continuous unrealized loss position 12 months or more, fair value	105,279	182,697
Continuous unrealized loss position 12 months or more, unrealized losses	(4,721)	(12,181)
Continuous unrealized loss position total, fair value	199,483	408,516
Continuous unrealized loss position total, unrealized losses	(6,765)	(17,572)
Corporate debt securities | Non-investment grade
Continuous unrealized loss position, fair values of investment securities available-for-sale
Continuous unrealized loss position less than 12 months, fair value	2,078
Continuous unrealized loss position less than 12 months, unrealized losses	(53)
Continuous unrealized loss position 12 months or more, fair value	13,386	12,574
Continuous unrealized loss position 12 months or more, unrealized losses	(6,681)	(7,558)
Continuous unrealized loss position total, fair value	15,464	12,574
Continuous unrealized loss position total, unrealized losses	$ (6,734)	$ (7,558)