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Repurchase of Shares - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2017 | Nov. 08, 2017 | Feb. 02, 2016
Equity, Class of Treasury Stock [Line Items] |  |  |
Repurchase of shares, Shares | 5,519 |  |
Average price at which ordinary shares are repurchased | $ 61.70 |  |
Remaining authority to repurchase outstanding ordinary shares | $ 256,261,000 |  |
February 2016 Plan [Member] |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |
Share repurchase program, Authorized amount |  |  | $ 750,000,000
Subsequent Event [Member] |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |
Share repurchase program, Authorized amount |  | $ 800,000,000 |

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- Definition Total cost of shares repurchased divided by the total number of shares repurchased. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655 + Details
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