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Pension and Other Post-Retirement Benefits - Plan assets (Details) - USD ($)
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Defined benefit plans      
Expected weighted-average long-term rate of return on plan assets 3.04% 3.00%  
Fair value measurement of pension plan assets:      
Fair value of plan assets at beginning of year $ 6,717,000 $ 6,665,000 $ 5,487,000
Estimated payments in 2019 $ 1,130,000    
Insurance contract      
Defined benefit plans      
Plan asset investment 100.00%    
Fair value measurement of pension plan assets:      
Fair value of plan assets at beginning of year $ 6,717,000 6,665,000  
Level 3 | Insurance contract      
Fair value measurement of pension plan assets:      
Fair value of plan assets at beginning of year $ 6,717,000 $ 6,665,000