Annual report pursuant to Section 13 and 15(d)

Loans and Allowance for Loan Losses (Details Textual)

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Loans and Allowance for Loan Losses (Details Textual) (USD $)
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Loans and Allowance for Loan Losses (Textual) [Abstract]      
Loans $ 2,966,847,000 $ 2,818,583,000 $ 2,837,253,000
Interest income 154,355,000 156,360,000 151,576,000
Total accruing interest 8,843,000 19,912,000  
Individually evaluated for impairment 5,911,000 10,053,000  
Loans and Allowance for Loan Losses (Additional Textual) [Abstract]      
Average investment in impaired loans 152,981,000 251,317,000 297,900,000
Interest income recorded on impaired loans 5,900,000 10,100,000 12,100,000
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  
Restructured loans 63,500,000    
Nonaccrual Loans [Member]
      
Loans and Allowance for Loan Losses (Textual) [Abstract]      
Loans 26,200,000 44,800,000  
Interest income 1,300,000 1,300,000 1,000,000
Total accruing interest 8,800,000 19,900,000  
Impaired loans [Member]
      
Loans and Allowance for Loan Losses (Textual) [Abstract]      
Loans 155,400,000 255,100,000  
Individually evaluated for impairment 142,400,000 242,800,000  
Impaired loans collectively evaluated $ 13,000,000 $ 12,300,000