Investment Securities (Details 3) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Available for sale:
Fair value, less than 12 months	$ 18,504	$ 1,269,409
Unrealized losses, less than 12 months	(840)	(23,870)
Fair value, 12 months or more	42,252	46,446
Unrealized losses, 12 months or more	(11,474)	(10,761)
Fair value, total	60,756	1,315,855
Unrealized losses, total	(12,314)	(34,631)
Residential mortgage-backed securities
Available for sale:
Fair value, less than 12 months	777	1,166,720
Unrealized losses, less than 12 months	(6)	(19,192)
Fair value, 12 months or more	41,688	46,028
Unrealized losses, 12 months or more	(11,294)	(10,654)
Fair value, total	42,465	1,212,748
Unrealized losses, total	(11,300)	(29,846)
Obligations of states and political subdivisions
Available for sale:
Fair value, less than 12 months	17,727	97,701
Unrealized losses, less than 12 months	(834)	(4,666)
Fair value, 12 months or more	502	355
Unrealized losses, 12 months or more	(167)	(95)
Fair value, total	18,229	98,056
Unrealized losses, total	(1,001)	(4,761)
Other equity securities
Available for sale:
Fair value, less than 12 months		4,988
Unrealized losses, less than 12 months		(12)
Fair value, 12 months or more	62	63
Unrealized losses, 12 months or more	(13)	(12)
Fair value, total	62	5,051
Unrealized losses, total	$ (13)	$ (24)