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Capital Management and Dividends - Additional Information (Detail) $ / shares in Units, $ / shares in Units, $ in Millions, $ in Millions | 2 Months Ended | 3 Months Ended | 12 Months Ended
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May 20, 2019 $ / shares | Sep. 30, 2016 USD ($) $ / shares shares | Sep. 30, 2016 AUD ($) $ / shares shares | Mar. 31, 2019 USD ($) | Mar. 31, 2018 | Mar. 31, 2017 USD ($)
Dividends Payable [Line Items] |  |  |  |  |  |
Aggregate cost of common stock repurchased | $ |  |  |  |  |  | $ 99.8
Ordinary dividend record date |  |  |  |  | Jun. 06, 2019 |
Ordinary dividend payment Date |  |  |  |  | Aug. 02, 2019 |
Subsequent Event [Member] |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |
Ordinary dividend declared (in dollars per share) | $ / shares | $ 0.26 |  |  |  |  |
Fiscal 2017 Program [Member] |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |
Aggregate cost of common stock repurchased |  | $ 99.8 | $ 131.4 | $ 100.0 |  |
Aggregate number of common stock repurchased and cancelled (in shares) | shares |  | 6,090,133 | 6,090,133 |  |  |
Average price paid per share of common stock repurchased and cancelled | (per share) |  | $ 16.40 | $ 21.58 |  |  |

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