Quarterly report pursuant to Section 13 or 15(d)

Loans and Allowance for Loan Losses (Details Textual)

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Loans and Allowance for Loan Losses (Details Textual) (USD $)
9 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Sep. 30, 2011
Sep. 30, 2012
Nonaccrual Loans [Member]
Sep. 30, 2011
Nonaccrual Loans [Member]
Sep. 30, 2012
Impaired loans [Member]
Dec. 31, 2011
Impaired loans [Member]
Loans and Allowance for Loan Losses (Textual) [Abstract]              
Loans $ 2,908,510,000 $ 2,818,583,000 $ 2,818,342,000 $ 32,200,000 $ 51,900,000 $ 177,900,000 $ 255,100,000
Total accruing interest 9,096,000 19,912,000   9,100,000 12,100,000    
Individually evaluated for impairment           161,200,000 242,800,000
Impaired loans collectively evaluated           16,700,000 12,300,000
TDR Recorded investment           63,800,000 112,600,000
Loans and Allowance for Loan Losses (Additional Textual) [Abstract]              
Contractually required payments 1,080,780            
Cash flows expected to be collected 1,072,726            
Fair value of loans acquired as on date of acquisition 1,052,358            
Restructured loans $ 1,400,000            
restructured loans, Number 3