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Accounts and Other Receivables - Provision for Doubtful Trade Debts (Detail) - USD ($)
$ in Millions
12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Balance at beginning of period $ 0.9 $ 1.1 $ 0.8
Adjustment to provision 0.6 (0.1) 0.5
Write-offs, net of recoveries (0.2) (0.1) (0.2)
Balance at end of period $ 1.3 $ 0.9 $ 1.1