Investment Securities (Details 3) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	$ (2,133,000)	$ (41,910,000)
Unrealized losses 12 months or more	(1,530,000)	(3,914,000)
Total unrealized losses	(3,663,000)	(45,824,000)
Fair value of unrealized losses less than 12 months	237,411,000	2,174,784,000
Fair value of unrealized losses 12 months or more	176,979,000	46,713,000
Fair value of total unrealized losses	414,390,000	2,221,497,000
Federal agency securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months		(25,000)
Unrealized losses 12 months or more		0
Total unrealized losses		(25,000)
Fair value of unrealized losses less than 12 months		29,716,000
Fair value of unrealized losses 12 months or more		0
Fair value of total unrealized losses		29,716,000
Obligations of state and political subdivisions (municipal securities)
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	(10,000)	(4,983,000)
Unrealized losses 12 months or more	(18,000)	(367,000)
Total unrealized losses	(28,000)	(5,350,000)
Fair value of unrealized losses less than 12 months	971,000	237,902,000
Fair value of unrealized losses 12 months or more	348,000	2,543,000
Fair value of total unrealized losses	1,319,000	240,445,000
Residential mortgage-related securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	(1,443,000)	(36,280,000)
Unrealized losses 12 months or more	(20,000)	(2,234,000)
Total unrealized losses	(1,463,000)	(38,514,000)
Fair value of unrealized losses less than 12 months	186,954,000	1,613,498,000
Fair value of unrealized losses 12 months or more	1,469,000	43,306,000
Fair value of total unrealized losses	188,423,000	1,656,804,000
Asset-backed securities
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	(9,000)	(621,000)
Unrealized losses 12 months or more	(698,000)	0
Total unrealized losses	(707,000)	(621,000)
Fair value of unrealized losses less than 12 months	4,091,000	293,568,000
Fair value of unrealized losses 12 months or more	174,640,000	0
Fair value of total unrealized losses	178,731,000	293,568,000
Other securities (debt and equity)
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	(671,000)	(1,000)
Unrealized losses 12 months or more	(794,000)	(1,313,000)
Total unrealized losses	(1,465,000)	(1,314,000)
Fair value of unrealized losses less than 12 months	45,395,000	100,000
Fair value of unrealized losses 12 months or more	522,000	864,000
Fair value of total unrealized losses	$ 45,917,000	$ 964,000