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Schedule of Net Periodic Benefit Cost (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Pension Benefits    
Net Period Benefit Cost Assumptions [Line Items]    
Service cost $ 30  
Interest cost 902  
Expected return on plan assets (483)  
Administrative expenses 1  
Net periodic pension cost 450  
Pension Benefits | Predecessor    
Net Period Benefit Cost Assumptions [Line Items]    
Service cost   $ 419
Interest cost   991
Expected return on plan assets   (601)
Administrative expenses   22
Payroll tax of net pension costs   56
Amortization of net actuarial losses   32
Recognized actuarial (benefit) loss   447
Net periodic pension cost   1,366
Other Benefits    
Net Period Benefit Cost Assumptions [Line Items]    
Service cost 15  
Interest cost 29  
Amortization of prior service cost (75)  
Recognized actuarial (benefit) loss 11  
Net periodic pension cost $ (20)  
Other Benefits | Predecessor    
Net Period Benefit Cost Assumptions [Line Items]    
Service cost   21
Interest cost   51
Amortization of prior service cost   (1,088)
Recognized actuarial (benefit) loss   (283)
Net periodic pension cost   $ (1,299)