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Executive Benefit Agreements, Employee Savings Plans and Collective Bargaining Agreements - Executive Benefit Agreements (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Compensation Related Costs [Abstract]
Total undiscounted death benefits	$ 2,424	$ 4,208
Total accrued death benefits	2,533	4,007
Total undiscounted executive benefits	191	201
Total accrued executive benefits	$ 191	$ 168