Premises and Equipment (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Premises and Equipment      
Premises and equipment, gross $ 116,371,000 $ 117,313,000  
Less accumulated depreciation 52,397,000 51,486,000  
Total premises and equipment 63,974,000 65,827,000  
Depreciation expense 5,600,000 5,500,000 5,400,000
Land and improvements      
Premises and Equipment      
Premises and equipment, gross 21,559,000 21,532,000  
Buildings and improvements      
Premises and Equipment      
Premises and equipment, gross 62,794,000 62,159,000  
Furniture and equipment      
Premises and Equipment      
Premises and equipment, gross $ 32,018,000 $ 33,622,000