Share-Based Payments - Summary of Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
Dec. 31, 2018 USD ($) $ / shares shares
Shares
Outstanding at October 1, 2018 \| shares	996
Granted \| shares	66
Exercised \| shares	(138)
Outstanding at December 31, 2018 \| shares	924
Exercisable at December 31, 2018 \| shares	836
Vested and expected to vest at December 31, 2018 \| shares	918
Weighted-average Exercise Price
Outstanding at October 1, 2017 (in dollars per share) \| $ / shares	$ 63.13
Granted (in dollars per share) \| $ / shares	185.05
Exercised (in dollars per share) \| $ / shares	54.69
Outstanding at December 31, 2017 (in dollars per share) \| $ / shares	73.16
Exercisable at December 31, 2017 (in dollars per share) \| $ / shares	61.99
Vested and expected to vest at December 31, 2016 (in dollars per share) \| $ / shares	$ 72.39
Weighted-average Remaining Contractual Term
Outstanding at December 31, 2018	2 years 8 months 20 days
Exercisable at December 31, 2018	2 years 3 months 20 days
Vested and expected to vest at December 31, 2018	2 years 8 months 13 days
Aggregate Intrinsic Value
Outstanding at December 31, 2018 \| $	$ 105,207
Exercisable at December 31, 2018 \| $	104,507
Vested and expected to vest at December 31, 2018 \| $	$ 105,161

Share-based Compensation Arrangement by Share-based Payment Award, Options, Aggregate Intrinsic Value [Abstract]

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Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Remaining Contractual Term [Abstract]

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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest exercisable or convertible options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of share options (or share units) exercised during the current period.

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