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Pension and Other Post Retirement Benefit Plans - Narrative (Details) - USD ($)
 12 Months Ended
Mar. 01, 2005
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]        
Percentage of employees covered by plan   10.00%    
Minimum participant attained age 55 years      
Requisite service period (at least) 10 years      
Decrease in funded status   $ 625,000    
Accumulated other comprehensive loss, net of tax   $ 1,700,000    
Decrease in discount rate   0.90%    
Discount rate   2.30% 3.20% 4.30%
Increase in liability   $ 6,800,000    
Liability reduction for mortality table updates   700,000    
Actual return on plan assets   7,925,000 $ 12,972,000  
Increase from expected return   3,800,000    
Accumulated benefit obligation   80,800,000 76,800,000  
Net periodic pension benefit cost   (1,419,000) (909,000) $ (1,693,000)
Minimum required contribution in next fiscal year   $ 0    
Requisite service period   1000 hours    
Employer percentage contribution   2.00%    
Vesting period   5 years    
Expense recognized in the period   $ 5,100,000 4,600,000 5,100,000
Fair value of plan assets   88,512,000 85,121,000 76,736,000
Level 1        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets   85,007,000 80,689,000  
Level 2        
Defined Benefit Plan Disclosure [Line Items]        
Fair value of plan assets   $ 3,505,000 4,432,000  
MBT        
Defined Benefit Plan Disclosure [Line Items]        
Requisite service period (at least)   5 years    
Defined benefit plan, benefit obligation   $ 3,500,000    
Post retirement plan expense   $ 126,000 $ 43,000  
Contribution for first 3%        
Defined Benefit Plan Disclosure [Line Items]        
Amount of discretionary contributions made by employer to defined contribution plan, percent   100.00%    
Maximum annual contribution percentage per employee   3.00%    
Contribution after first 3%        
Defined Benefit Plan Disclosure [Line Items]        
Amount of discretionary contributions made by employer to defined contribution plan, percent   50.00%    
Maximum annual contribution percentage per employee   3.00%    
Minimum | MBT        
Defined Benefit Plan Disclosure [Line Items]        
Age of plan participants   55 years    
Minimum | Debt securities        
Defined Benefit Plan Disclosure [Line Items]        
Maturities of debt securities   15 days 15 days  
Maximum | MBT        
Defined Benefit Plan Disclosure [Line Items]        
Age of plan participants   65 years    
Maximum | Debt securities        
Defined Benefit Plan Disclosure [Line Items]        
Maturities of debt securities   6 years 8 months 8 days 7 years 8 months 1 day  
Weighted Average | Debt securities        
Defined Benefit Plan Disclosure [Line Items]        
Maturities of debt securities   3 years 7 months 24 days 4 years  
Non-qualified plans        
Defined Benefit Plan Disclosure [Line Items]        
Net periodic pension benefit cost   $ 165,000 $ 192,000 $ 161,000