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Pension and Employee Benefit Plans - Additional Information (Detail) - USD ($)
9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan contributions $ 1,600,000 $ 29,000  
Unfunded liability plans 9,600,000   $ 11,100,000
Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Anticipated contribution to fund the pension plan during the reminder of the fiscal year 300,000    
Health Care Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Anticipated contribution to fund the pension plan during the reminder of the fiscal year $ 25,000