Commitments and Contingencies (Details Textual) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Commitments and Contingencies (Textual) [Abstract]
Lines of credit	$ 1,980,000,000
Commitments and Contingencies Additional (Textual) [Abstract]
Commitments to extend credit	585,200,000	570,100,000
Obligations under letters of credit	66,800,000	70,400,000
Reserve for undisbursed commitments	9,600,000	10,500,000
Lines of credit	1,980,000,000
Secured [Member]
Commitments and Contingencies (Textual) [Abstract]
Lines of credit	1,570,000,000
Commitments and Contingencies Additional (Textual) [Abstract]
Lines of credit	$ 1,570,000,000