INVESTMENT SECURITIES, Available-For-Sale Portfolio (Details) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2011		Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 3,200,187,000		$ 2,900,410,000
Gross Unrealized Gains	32,342,000		24,383,000
Gross Unrealized Losses	(26,421,000)		(48,852,000)
Fair Value	3,206,108,000		2,875,941,000
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,870,000		19,847,000
Gross Unrealized Gains	755,000		607,000
Gross Unrealized Losses	0		0
Fair Value	20,625,000		20,454,000
US Government Agencies and Government Sponsored Enterprise Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,206,670,000		1,349,289,000
Gross Unrealized Gains	2,744,000		2,297,000
Gross Unrealized Losses	(3,794,000)		(18,121,000)
Fair Value	1,205,620,000		1,333,465,000
Commercial Mortgage Backed Securities Issued By US Government Agencies And Government Sponsored Enterprise [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,709,000		18,620,000
Gross Unrealized Gains	625,000		512,000
Gross Unrealized Losses	0		0
Fair Value	24,334,000		19,132,000
Residential Mortgage Backed Securities Issued By US Government Agencies And Government Sponsored Enterprise [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	746,942,000		295,140,000
Gross Unrealized Gains	18,660,000		11,574,000
Gross Unrealized Losses	(304,000)		0
Fair Value	765,298,000		306,714,000
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32,145,000		0
Gross Unrealized Gains	822,000		0
Gross Unrealized Losses	(87,000)		0
Fair Value	32,880,000		0
Other Residential Mortgage-Backed Securities [Member] | Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0		0
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Fair Value	0		0
Other Residential Mortgage-Backed Securities [Member] | Non-investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0		14,996,000
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		(8,742,000)
Fair Value	0		6,254,000
Corporate Debt Securities [Member] | Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,125,985,000		1,056,537,000
Gross Unrealized Gains	8,390,000		9,095,000
Gross Unrealized Losses	(12,540,000)		(8,765,000)
Fair Value	1,121,835,000		1,056,867,000
Corporate Debt Securities [Member] | Non-investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	26,181,000	[1]	50,015,000
Gross Unrealized Gains	0	[1]	31,000
Gross Unrealized Losses	(9,684,000)	[1]	(11,316,000)
Fair Value	16,497,000	[1]	38,730,000
Other than temporary impairment , pre-tax basis, credit portion recognized in earnings			16,700,000
Other than temporary impairment , pre-tax basis, non-credit portion recognized in other comprehensive income	5,100,000		15,400,000
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,685,000		95,966,000
Gross Unrealized Gains	346,000		267,000
Gross Unrealized Losses	(12,000)		(1,908,000)
Fair Value	$ 19,019,000		$ 94,325,000

[1] For the six months ended June 30, 2011, the Company recorded $464 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 $16.7 million, on a pre-tax basis, of the credit portion of OTTI through earnings and $15.4 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, 2010.