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Schedule of Net Periodic Benefit Cost for Postretirement Health Care and Life Insurance Plan (Detail) - Other Benefits - USD ($)
$ in Thousands
 4 Months Ended 5 Months Ended 12 Months Ended
Jul. 31, 2017
Dec. 31, 2017
Mar. 31, 2017
Net Period Benefit Cost Assumptions [Line Items]      
Service cost   $ 29  
Interest cost   75  
Net periodic pension cost   $ 104  
Predecessor      
Net Period Benefit Cost Assumptions [Line Items]      
Service cost $ 23   $ 81
Interest cost 64   201
Amortization of prior service cost (927)   (4,346)
Amortization of net (loss) gain (335)   (1,138)
Net periodic pension cost $ (1,175)   $ (5,202)