INVESTMENT SECURITIES (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended
	Mar. 31, 2012		Mar. 31, 2011	Dec. 31, 2011
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	$ 2,737,687			$ 3,132,968
Gross Unrealized Gains	48,265			47,356
Gross Unrealized Losses	(79,232)			(107,746)
Fair Value	2,706,720			3,072,578
Other than temporary impairment, pre-tax basis, credit portion recognized in earnings	99			633
Other than temporary impairment, pre-tax basis, non-credit portion recognized in other comprehensive income	5,066		5,091	5,100
U.S. Treasury securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	19,903			19,892
Gross Unrealized Gains	715			833
Fair Value	20,618			20,725
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	514,003			575,148
Gross Unrealized Gains	844			1,709
Gross Unrealized Losses	(525)			(279)
Fair Value	514,322			576,578
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	46,248			46,008
Gross Unrealized Gains	3,135			3,307
Fair Value	49,383			49,315
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	893,214			963,688
Gross Unrealized Gains	31,786			30,854
Gross Unrealized Losses	(369)			(772)
Fair Value	924,631			993,770
Municipal securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	78,414			76,255
Gross Unrealized Gains	4,358			3,696
Gross Unrealized Losses				(5)
Fair Value	82,772			79,946
Corporate debt securities | Investment grade
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	1,151,013			1,411,409
Gross Unrealized Gains	7,227			6,762
Gross Unrealized Losses	(67,631)			(95,610)
Fair Value	1,090,609			1,322,561
Corporate debt securities | Non-investment grade
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	24,616	[1]		30,693	[1]
Gross Unrealized Gains	13	[1]
Gross Unrealized Losses	(10,707)	[1]		(11,078)	[1]
Fair Value	13,922	[1]		19,615	[1]
Other securities
Schedule of Available-for-sale Securities
Investment securities available-for-sale, amortized cost	10,276			9,875
Gross Unrealized Gains	187			195
Gross Unrealized Losses				(2)
Fair Value	$ 10,463			$ 10,068

[1] For the three months ended March 31, 2012, 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. The Company recorded $633 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 and other mortgage-backed securities in other comprehensive income for the year ended December 31, 2011.