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Retirement Plans - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]      
Defined contribution retirement plan voluntary contributions $ 18,000    
Retirement benefit obligations     $ 13,796,000
Retirement benefit obligations discount rate 3.76% 3.96%  
Expected actuarial losses included in accumulated other comprehensive loss in net periodic benefit cost in 2017 $ 104,000    
Net periodic pension cost 0 $ 0 (26,000)
Accumulated benefit obligation 0 0  
Accumulated other comprehensive income     $ 623,000
Former Executives      
Defined Benefit Plan Disclosure [Line Items]      
Retirement benefit obligations 6,900,000 $ 6,500,000  
Employees 50 years or over      
Defined Benefit Plan Disclosure [Line Items]      
Defined contribution retirement plan voluntary contributions $ 24,000