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Employee Benefit Plans - Summary of Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Pension Plan [Member]    
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income    
Net actuarial (gain) loss $ 191,102 $ (3,395,903)
Recognized actuarial (gain) loss due to settlements 801,622 636,121
Total recognized in other comprehensive income (before tax effects) 992,724 (2,759,782)
Total recognized in net benefit cost and other comprehensive income (before tax effects) 219,384 (3,999,150)
Supplemental Employee Retirement Plan [Member]    
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income    
Net actuarial (gain) loss (540,666) 836,680
Total recognized in other comprehensive income (before tax effects) (540,666) 836,680
Total recognized in net benefit cost and other comprehensive income (before tax effects) $ (221,523) 1,176,942
Postretirement Benefits [Member]    
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income    
Net actuarial (gain) loss   (67,772)
Recognized actuarial (gain) loss   2,079
Prior service cost (credit)   (1,678,920)
Prior service cost (credit) due to curtailment   1,678,920
Recognized actuarial (gain) loss due to settlements   169,089
Total recognized in other comprehensive income (before tax effects)   103,396
Total recognized in net benefit cost and other comprehensive income (before tax effects)   $ (1,708,563)