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Schedule of Net Periodic Benefit Cost (Detail) - USD ($)
$ in Thousands
 3 Months Ended 4 Months Ended 5 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jul. 31, 2017
Dec. 31, 2017
Jun. 30, 2018
Jun. 30, 2017
Mar. 31, 2017
Pension Benefits              
Net Period Benefit Cost Assumptions [Line Items]              
Service cost $ 41     $ 546 $ 71    
Interest cost 882     1,599 1,784    
Expected return on plan assets (482)     (882) (964)    
Administrational expenses 2     19 3    
Payroll tax of net pension costs       29      
Amortization of net actuarial losses       131      
Curtailment gain       (99)      
Settlement loss recognized 335       335    
Net periodic pension cost 778     1,343 1,229    
Pension Benefits | Predecessor              
Net Period Benefit Cost Assumptions [Line Items]              
Service cost   $ 294 $ 393     $ 713 $ 1,182
Interest cost   984 1,313     1,975 3,814
Expected return on plan assets   (518) (691)     (1,119) (2,246)
Administrational expenses   2 3     24 28
Payroll tax of net pension costs           56 56
Amortization of net actuarial losses           32 32
Recognized actuarial benefit   561 748     1,008 1,785
Net periodic pension cost   1,323 1,766     2,689 4,651
Other Benefits              
Net Period Benefit Cost Assumptions [Line Items]              
Service cost 15     29 30    
Interest cost 29     75 58    
Amortization of prior service cost (75)       (150)    
Recognized actuarial benefit 11       22    
Net periodic pension cost $ (20)     $ 104 $ (40)    
Other Benefits | Predecessor              
Net Period Benefit Cost Assumptions [Line Items]              
Service cost   17 23     38 81
Interest cost   48 64     99 201
Amortization of prior service cost   (695) (927)     (1,783) (4,346)
Recognized actuarial benefit   (252) (335)     (535) (1,138)
Net periodic pension cost   $ (882) $ (1,175)     $ (2,181) $ (5,202)