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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
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May 18, 2017 $ / shares | Mar. 31, 2017 | Sep. 30, 2016 USD ($) $ / shares shares | Sep. 30, 2016 AUD AUD / shares shares | Mar. 31, 2017 USD ($) | Mar. 31, 2016 USD ($) | Mar. 31, 2015 USD ($)
Dividends Payable [Line Items] |  |  |  |  |  |  |
Aggregate cost of common stock repurchased | $ |  |  |  |  | $ 99.8 | $ 22.3 | $ 9.1
Ordinary dividend record date |  | Jun. 08, 2017 |  |  |  |  |
Ordinary dividend payment Date |  | Aug. 04, 2017 |  |  |  |  |
Subsequent Event [Member] |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |
Ordinary dividend declared | $ / shares | $ 28.0 |  |  |  |  |  |
Fiscal 2017 Program [Member] |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |
Aggregate cost of common stock repurchased |  |  | $ 99.8 | AUD 131.4 | $ 100.0 |  |
Aggregate number of common stock repurchased and cancelled | shares |  |  | 6,090,133 | 6,090,133 |  |  |
Average price paid per share of common stock repurchased and cancelled | (per share) |  |  | $ 16.40 | AUD 21.58 |  |  |

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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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