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Summary of Deferred Stock Unit Activity (Detail) - $ / shares
4 Months Ended 12 Months Ended
Jul. 31, 2017
Mar. 31, 2017
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]    
Weighted-average Grant-Date Fair Value, Retirement distribution $ 24.19 $ 6.83
Number of Shares, Retirement distribution (350,838) (12,792)
Predecessor    
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]    
Weighted-average Grant-Date Fair Value, Beginning Balance Outstanding $ 24.19 $ 23.58
Weighted-average Grant-Date Fair Value, Ending Balance Outstanding   $ 24.19
Number of Shares Beginning Balance Outstanding 350,838 363,630
Number of Shares Ending Balance Outstanding   350,838