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Retirement Plans - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]    
Defined contribution retirement plan voluntary contributions $ 18,500  
Retirement benefit obligations discount rate 3.98% 3.33%
Expected actuarial losses included in accumulated other comprehensive loss in net periodic benefit cost in 2019 $ 84,000  
Former Executives    
Defined Benefit Plan Disclosure [Line Items]    
Retirement benefit obligations 6,600,000 $ 7,300,000
Employees 50 years or over    
Defined Benefit Plan Disclosure [Line Items]    
Defined contribution retirement plan voluntary contributions $ 24,500