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Capital Management and Dividends - Additional Information (Detail) AUD / shares in Units, $ / shares in Units, AUD in Millions, $ in Millions |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
May. 19, 2016 $ / shares | Mar. 31, 2016 | Sep. 30, 2015 USD ($) $ / shares shares | Sep. 30, 2015 AUD AUD / shares shares | Mar. 31, 2016 USD ($) | Mar. 31, 2015 USD ($) | Mar. 31, 2014 USD ($)
Dividends Payable [Line Items] |  |  |  |  |  |  |
Percentage of stock buyback program authorized |  | 5.00% |  |  | 5.00% |  |
Aggregate number of common stock repurchased and cancelled | shares |  |  | 1,653,247 | 1,653,247 |  |  |
Aggregate cost of common stock repurchased |  |  | $ 22.3 | AUD 30.0 | $ 22.3 | $ 9.1 | $ 22.1
Average price paid per share of common stock repurchased and cancelled | (per share) |  |  | $ 13.50 | AUD 18.14 |  |  |
Ordinary dividend record date |  | Jun. 09, 2016 |  |  |  |  |
Ordinary dividend payment Date |  | Aug. 05, 2016 |  |  |  |  |
Subsequent Event [Member] |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |
Ordinary dividend declared | $ / shares | $ 0.29 |  |  |  |  |  |
Fiscal 2017 Program [Member] |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |
Aggregate cost of common stock repurchased | $ |  |  |  |  | $ 100.0 |  |

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