Equity-Based Compensation - Summary of Stock Options Activity (Details) shares in Thousands	12 Months Ended
Sep. 30, 2018 $ / shares shares
Stock Options
Outstanding at October 1, 2017	5,747
Vested and exercisable at September 30, 2018	2,175
Expected to vest after September 30, 2018	3,572
Weighted Average Exercise Price, Stock Options
Weighted Average Exercise Price, Outstanding at October 1, 2017 \| $ / shares	$ 22.00
Weighted Average Exercise Price, Expected to vest after September 30, 2018 \| $ / shares	$ 22.00
IPO
Stock Options
Grants in connection with the IPO	5,747
Weighted Average Exercise Price, Stock Options
Weighted Average Exercise Price, Grants in connection with the IPO \| $ / shares	$ 22.00

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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

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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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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 exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. 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 per share amount at which grantees can acquire shares of common stock by exercise of options.

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