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Accounts and Other Receivables - Provision for Doubtful Trade Debts (Detail) - USD ($)
$ in Millions
12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Mar. 31, 2017
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Balance at beginning of period $ 1.3 $ 0.9 $ 1.1
Adjustment to provision 2.8 0.6 (0.1)
Write-offs, net of recoveries (1.2) (0.2) (0.1)
Balance at end of period $ 2.9 $ 1.3 $ 0.9