Investment Securities (Details 4) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Held To Maturity Securities Continuous Unrealized Loss Position [Abstract]
Held to maturity, Estimated fair value, Less than 12 months	$ 22,913	$ 76,318
Held to maturity, Unrealized Losses, Less than 12 months	(231)	(638)
Held to maturity, Estimated fair value, 12 months or more	185,421	198,607
Held to maturity, Unrealized Losses, 12 months or more	(102,533)	(114,453)
Investment securities in continuous unrealized loss position
Investment securities continuous unrealized loss position less than twelve months aggregate losses	863,732	256,940
Total of investment securities, unrealized losses, less than 12 months	(6,440)	(13,497)
Total of investment securities, fair value, more than 12 months	1,175,049	1,379,002
Total of investment securities, unrealized losses, more than 12 months	(344,405)	(413,331)
Obligations of states and political subdivisions [Member]
Held To Maturity Securities Continuous Unrealized Loss Position [Abstract]
Held to maturity, Estimated fair value, Less than 12 months	22,591	76,318
Held to maturity, Unrealized Losses, Less than 12 months	(108)	(638)
Held to maturity, Estimated fair value, 12 months or more	451	467
Held to maturity, Unrealized Losses, 12 months or more	(41)	(56)
Privately Issued Mortgage Backed Securities [Member]
Held To Maturity Securities Continuous Unrealized Loss Position [Abstract]
Held to maturity, Estimated fair value, Less than 12 months	322	0
Held to maturity, Unrealized Losses, Less than 12 months	(123)	0
Held to maturity, Estimated fair value, 12 months or more	184,970	198,140
Held to maturity, Unrealized Losses, 12 months or more	$ (102,492)	$ (114,397)