Investment Securities, Available-for-Sale (Details 2) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Investments with an unrealized loss position
Fair Value Less than Twelve Months	$ 293,986	$ 730,089
Fair Value Twelve Months or More	30,554	39,021
Fair Value, Total	324,540	769,110
Unrealized Loss Less than Twelve Months	(3,835)	(16,265)
Unrealized Loss Twelve Months or More	(4,470)	(7,048)
Unrealized Loss, Total	(8,305)	(23,313)
State and local governments and other issues [Member]
Investments with an unrealized loss position
Fair Value Less than Twelve Months	129,535	365,164
Fair Value Twelve Months or More	13,671	13,122
Fair Value, Total	143,206	378,286
Unrealized Loss Less than Twelve Months	(2,546)	(14,680)
Unrealized Loss Twelve Months or More	(1,095)	(1,264)
Unrealized Loss, Total	(3,641)	(15,944)
Collateralized debt obligations [Member]
Investments with an unrealized loss position
Fair Value Less than Twelve Months	0	0
Fair Value Twelve Months or More	5,953	6,595
Fair Value, Total	5,953	6,595
Unrealized Loss Less than Twelve Months	0	0
Unrealized Loss Twelve Months or More	(2,985)	(4,583)
Unrealized Loss, Total	(2,985)	(4,583)
Residential Mortgage Backed Securities [Member]
Investments with an unrealized loss position
Fair Value Less than Twelve Months	164,451	364,925
Fair Value Twelve Months or More	10,930	19,304
Fair Value, Total	175,381	384,229
Unrealized Loss Less than Twelve Months	(1,289)	(1,585)
Unrealized Loss Twelve Months or More	(390)	(1,201)
Unrealized Loss, Total	$ (1,679)	$ (2,786)