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Executive Benefit Agreements, Employee Savings Plans and Collective Bargaining Agreements - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2017
USD ($)
Person
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]  
Minimum amount of life insurance policies to be kept by the company for 2005 Agreement | $ $ 2,500,000
Collective Bargaining Agreements [Member]  
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]  
Number of persons employed 569
Number of persons represented by union under agreements 166
Collective Bargaining Agreements [Member] | Minimum [Member]  
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]  
Union agreement expiration date 2018-07
Collective Bargaining Agreements [Member] | Maximum [Member]  
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]  
Union agreement expiration date 2019-11