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Benefit Plans Narrative (Details) (USD $)
12 Months Ended
Dec. 31, 2012
Y
Dec. 31, 2011
Dec. 31, 2010
Pension Plans [Abstract]      
Number of compensation years included in benefit calculation 3    
Expected future working lifetime of participants 12 years 5 months 12 days    
Market gains (losses) $ (649,000) $ 303,000  
Return on investments since plan inception, percent 11.10%    
Investments benchmark since inception, percent 10.30%    
Return on investments for 2012, percent 12.60%    
Investments benchmark for 2012, percent 11.50%    
Flexible Spending Plan [Abstract]      
Annual maximum contribution limit under Health Care Spending Account plan 2,500    
Annual maximum contribution limit under Dependent Care Spending Account plan 5,000    
Deferral Plan [Abstract]      
Employer contributions to deferral plan 1,044,000 1,001,000 962,000
Fixed Income Funds [Member]
     
Pension Plans [Abstract]      
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum 25.00%    
Bonds [Member]
     
Pension Plans [Abstract]      
Actual plan asset allocations 45.00%    
Cash and Cash Equivalents [Member]
     
Pension Plans [Abstract]      
Actual plan asset allocations 8.00%    
Equity Securities [Member]
     
Pension Plans [Abstract]      
Actual plan asset allocations 47.00%    
Minimum [Member]
     
Pension Plans [Abstract]      
Period for performance standards 3 years    
Maximum [Member]
     
Pension Plans [Abstract]      
Period for performance standards 5 years    
Maximum [Member] | Private Corporation Assets [Member]
     
Pension Plans [Abstract]      
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum 5.00%    
Executive Supplemental Retirement Plan [Member]
     
Pension Plans [Abstract]      
Projected benefit obligation 13,130,000 11,726,000  
Net periodic pension cost 1,386,000 1,241,000 1,209,000
Executives and Non-employee Directors [Member] | Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits [Member]
     
Special Deferral Election Plan and Deferral Election Program [Abstract]      
Deferrals by executives and non-employee directors 2,501,000 2,306,000 2,103,000
Deferred compensation expense $ 88,000 $ 117,000 $ 98,000