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Repurchase of Shares - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2020 | Nov. 12, 2019 | Nov. 08, 2017
Equity, Class of Treasury Stock [Line Items] |  |  |
Repurchase of shares, Shares | 5,668 |  |
Average price at which ordinary shares are repurchased | $ 63.66 |  |
Share Repurchase Program 2017 Plan [Member] |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |
Share repurchase program, Authorized amount |  |  | $ 800,000,000
Share Repurchase Program 2019 Plan [Member] |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |
Share repurchase program, Authorized amount |  | $ 800,000,000 |
Remaining authority to repurchase outstanding ordinary shares | $ 678,344,000 |  |

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