INVESTMENT SECURITIES (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2012		Mar. 31, 2013
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost		$ 2,599,018,000		$ 2,578,384,000
Gross Unrealized Gains		34,739,000		28,610,000
Gross Unrealized Losses		(26,728,000)		(18,001,000)
Fair Value		2,607,029,000		2,588,993,000
Other than temporary impairment, pre-tax basis, credit portion recognized in earnings	99,000	99,000
Other than temporary impairment, pre-tax basis, non-credit portion recognized in other comprehensive income		5,100,000
U.S. Treasury securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost		459,613,000		469,747,000
Gross Unrealized Gains		1,135,000		1,048,000
Gross Unrealized Losses		(71,000)		(31,000)
Fair Value		460,677,000		470,764,000
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		197,264,000		197,137,000
Gross Unrealized Gains		673,000		520,000
Gross Unrealized Losses		(82,000)		(120,000)
Fair Value		197,855,000		197,537,000
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		174,036,000		142,050,000
Gross Unrealized Gains		6,665,000		3,405,000
Gross Unrealized Losses		(36,000)		(411,000)
Fair Value		180,665,000		145,044,000
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		1,123,880,000		1,018,638,000
Gross Unrealized Gains		20,883,000		18,078,000
Gross Unrealized Losses		(678,000)		(1,301,000)
Fair Value		1,144,085,000		1,035,415,000
Municipal securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost		163,333,000		206,113,000
Gross Unrealized Gains		4,491,000		3,284,000
Gross Unrealized Losses		(731,000)		(2,639,000)
Fair Value		167,093,000		206,758,000
Corporate debt securities | Investment grade
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost		429,318,000		458,534,000
Gross Unrealized Gains		237,000		1,554,000
Gross Unrealized Losses		(17,572,000)		(6,765,000)
Fair Value		411,983,000		453,323,000
Corporate debt securities | Non-investment grade
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost		24,620,000	[1]	24,534,000	[1]
Gross Unrealized Gains		355,000	[1]	200,000	[1]
Gross Unrealized Losses		(7,558,000)	[1]	(6,734,000)	[1]
Fair Value		17,417,000	[1]	18,000,000	[1]
Other securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost		9,955,000		10,633,000
Gross Unrealized Gains		215,000		160,000
Fair Value		10,170,000		10,793,000
Other commercial mortgage-backed securities: | Investment grade
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost		16,999,000		50,998,000
Gross Unrealized Gains		85,000		361,000
Fair Value		$ 17,084,000		$ 51,359,000

[1] For the three months ended March 31, 2013, the Company did not record any OTTI. The Company recorded $99 thousand, on a pre-tax basis, of the credit portion of OTTI through earnings and $5.1 million of the non-credit portion of OTTI for pooled trust preferred securities in other comprehensive income for the year ended December 31, 2012.