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Employee Benefit Plans - Additional Information (Detail)
NOK in Millions
 1 Months Ended 2 Months Ended 3 Months Ended 4 Months Ended 6 Months Ended
Jul. 31, 2017
USD ($)
Apr. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2016
USD ($)
Jul. 31, 2017
USD ($)
Jul. 31, 2017
NOK
Sep. 30, 2017
USD ($)
Sep. 30, 2016
USD ($)
Sep. 30, 2016
NOK
Dec. 31, 2017
USD ($)
Pension Plans, Defined Benefit                    
Defined Benefit Plan Disclosure [Line Items]                    
Defined benefit plan, employer contributions     $ 0 $ 3,000,000       $ 3,000,000    
Expected contribution to the plan during the remaining quarters of fiscal 2018     0       $ 0      
Pension Plans, Defined Benefit | Predecessor                    
Defined Benefit Plan Disclosure [Line Items]                    
Defined benefit plan, employer contributions         $ 0          
Supplemental Executive Retirement Plan                    
Defined Benefit Plan Disclosure [Line Items]                    
Defined benefit plan, employer contributions     100,000 $ 100,000       100,000    
Expected contribution to the plan during the remaining quarters of fiscal 2018     $ 0       $ 0      
Retirement benefit plan, description             In 1991, the company adopted a Supplemental Executive Retirement Plan (“SERP”) for certain employees. The SERP provides for retirement benefits payable in the form of a joint and survivor annuity, equivalent installments, or a lump sum. In general, the SERP provides pension benefits determined based on the average of the participant’s highest compensation for any consecutive five year period during the ten years immediately preceding retirement multiplied by the participant’s benefit service.      
Supplemental Executive Retirement Plan | Predecessor                    
Defined Benefit Plan Disclosure [Line Items]                    
Defined benefit plan, employer contributions         0          
Supplemental Executive Retirement Plan | Scenario, Forecast                    
Defined Benefit Plan Disclosure [Line Items]                    
Settlement of distribution   $ 9,600,000                
Settlement loss   $ 500,000                
Norway’s Defined Benefit Pension Plan                    
Defined Benefit Plan Disclosure [Line Items]                    
Defined benefit plan, employer contributions $ 0       $ 400,000 NOK 3.0   $ 500,000 NOK 3.4  
Norway’s Defined Benefit Pension Plan | Scenario, Forecast                    
Defined Benefit Plan Disclosure [Line Items]                    
Expected contribution to the plan during the remaining quarters of fiscal 2018                   $ 0