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 $)
3 Months Ended 12 Months Ended 3 Months Ended 3 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Mar. 31, 2012
Mar. 31, 2012
Commercial Real Estate - Owner Occupied [Member]
Mar. 31, 2013
Commercial Real Estate - Owner Occupied [Member]
Dec. 31, 2012
Commercial Real Estate - Owner Occupied [Member]
Mar. 31, 2013
Nonaccrual Loans [Member]
Dec. 31, 2012
Nonaccrual Loans [Member]
Mar. 31, 2012
Nonaccrual Loans [Member]
Mar. 31, 2013
Impaired loans [Member]
Dec. 31, 2012
Impaired loans [Member]
Loans and Allowance for Loan Losses (Textual) [Abstract]                      
Loans $ 2,973,547,000 $ 2,966,847,000 $ 2,841,758,000   $ 512,029,000 $ 513,671,000 $ 23,000,000 $ 26,200,000 $ 42,400,000 $ 145,700,000 $ 155,400,000
Loans and interest accrued 90 days past due 6,187,000 8,843,000 12,267,000   304,000 1,711,000          
Collectively evaluated for impairment                   11,800,000 13,000,000
Individually evaluated for impairment 1,348,000 5,911,000               133,900,000 142,400,000
Restructured loans that defaulted in the current period       453,000              
Loans and Allowance for Loan Losses (Additional Textual) [Abstract]                      
Nonaccrual loans excluded from impaired loan 0   0                
Contractually required payments 1,080,780,000                    
Cash flows expected to be collected 1,072,726,000                    
Fair value of loans acquired as on date of acquisition 1,052,358,000                    
Debt restructurings $ 54,700,000 $ 63,500,000