INVESTMENT SECURITIES (Details) (USD $)	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	$ 2,596,823,000		$ 2,786,490,000
Gross Unrealized Gains	19,930,000		12,203,000
Gross Unrealized Losses	(24,086,000)		(64,896,000)
Fair Value	2,592,667,000		2,733,797,000
OTTI credit losses	115,500,000		115,500,000		115,500,000	115,500,000
U.S. Treasury securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	605,672,000		495,053,000
Gross Unrealized Gains	328,000		201,000
Gross Unrealized Losses	(2,353,000)		(3,622,000)
Fair Value	603,647,000		491,632,000
U.S. government agency and U.S. government sponsored enterprise debt securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	416,746,000		406,807,000
Gross Unrealized Gains	522,000		242,000
Gross Unrealized Losses	(4,287,000)		(12,726,000)
Fair Value	412,981,000		394,323,000
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	125,933,000		182,257,000
Gross Unrealized Gains	1,188,000		1,062,000
Gross Unrealized Losses	(1,554,000)		(4,449,000)
Fair Value	125,567,000		178,870,000
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	757,637,000		892,435,000
Gross Unrealized Gains	8,003,000		7,729,000
Gross Unrealized Losses	(8,058,000)		(14,927,000)
Fair Value	757,582,000		885,237,000
Municipal securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	293,148,000		297,390,000
Gross Unrealized Gains	5,984,000		1,122,000
Gross Unrealized Losses	(2,535,000)		(17,533,000)
Fair Value	296,597,000		280,979,000
Other residential mortgage-backed securities: | Investment grade
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	54,949,000	[1]	48,129,000	[1]
Gross Unrealized Gains	665,000	[1]
Gross Unrealized Losses	(356,000)	[1]	(1,802,000)	[1]
Fair Value	55,258,000	[1]	46,327,000	[1]
Other commercial mortgage-backed securities: | Investment grade
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	51,000,000	[1]	51,000,000	[1]
Gross Unrealized Gains	127,000	[1]	617,000	[1]
Fair Value	51,127,000	[1]	51,617,000	[1]
Corporate debt securities | Investment grade
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	211,143,000	[1]	312,726,000	[1]
Gross Unrealized Gains	1,127,000	[1]	613,000	[1]
Gross Unrealized Losses	(1,445,000)	[1]	(3,344,000)	[1]
Fair Value	210,825,000	[1]	309,995,000	[1]
Corporate debt securities | Non-investment grade
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	19,937,000	[1]	20,668,000	[1]
Gross Unrealized Gains	802,000	[1]	62,000	[1]
Gross Unrealized Losses	(2,963,000)	[1]	(5,629,000)	[1]
Fair Value	17,776,000	[1]	15,101,000	[1]
Other securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	60,658,000		80,025,000
Gross Unrealized Gains	1,184,000		555,000
Gross Unrealized Losses	(535,000)		(864,000)
Fair Value	$ 61,307,000		$ 79,716,000

[1] Investment securities rated BBB- or higher by S&P or Baa3 or higher by Moody's are considered investment grade. Conversely, investment securities rated lower than BBB- by S&P or lower than Baa3 by Moody's are considered non-investment grade.