Investment Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	$ (972)	$ (2,133)
Unrealized losses 12 months or more	(859)	(1,530)
Total unrealized losses	(1,831)	(3,663)
Fair value of unrealized losses less than 12 months	215,428	237,411
Fair value of unrealized losses 12 months or more	141,805	176,979
Fair value of total unrealized losses	357,233	414,390
US Treasury Securities [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	(4)
Unrealized losses 12 months or more	0
Total unrealized losses	(4)
Fair value of unrealized losses less than 12 months	1,001
Fair value of unrealized losses 12 months or more	0
Fair value of total unrealized losses	1,001
Obligations of state and political subdivisions [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	(241)	(10)
Unrealized losses 12 months or more	(17)	(18)
Total unrealized losses	(258)	(28)
Fair value of unrealized losses less than 12 months	15,070	971
Fair value of unrealized losses 12 months or more	348	348
Fair value of total unrealized losses	15,418	1,319
Residential mortgage-related securities [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	(673)	(1,443)
Unrealized losses 12 months or more	(206)	(20)
Total unrealized losses	(879)	(1,463)
Fair value of unrealized losses less than 12 months	179,764	186,954
Fair value of unrealized losses 12 months or more	3,153	1,469
Fair value of total unrealized losses	182,917	188,423
Asset-backed securities [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	(8)	(9)
Unrealized losses 12 months or more	(445)	(698)
Total unrealized losses	(453)	(707)
Fair value of unrealized losses less than 12 months	3,769	4,091
Fair value of unrealized losses 12 months or more	137,982	174,640
Fair value of total unrealized losses	141,751	178,731
Other securities (debt and equity) [Member]
Unrealized losses and fair value of available for sale securities , by investment category and time length
Unrealized losses less than 12 months	(46)	(671)
Unrealized losses 12 months or more	(191)	(794)
Total unrealized losses	(237)	(1,465)
Fair value of unrealized losses less than 12 months	15,824	45,395
Fair value of unrealized losses 12 months or more	322	522
Fair value of total unrealized losses	$ 16,146	$ 45,917