Equity-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Mar. 31, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at beginning of period (shares)	2,138,500
Granted (shares)	1,499,916
Exercised (shares)	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	(51,500)
Outstanding at end of period (shares)	3,586,916
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding at beginning of period, weighted average exercise price (in USD per share)	$ 21.63	$ 13.13
Granted, weighted average exercise price (in USD per share)	21.45
Exercised, weighted average exercise price (in USD per share)	0
Forfeited, weighted average exercise price (in USD per share)	16.59
Outstanding at end of period, weighted average exercise price (in USD per share)	21.63	$ 13.13
Granted, weighted average grant date fair value (in USD per share)	$ 6.91
Options exercisable at end of period (shares)	0
Unrecognized compensation expense related to unvested options at end of period	$ 15,901
Period for recognition of unrecognized compensation cost	2 years 7 months 6 days

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

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- Definition

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.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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- Definition

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

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No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

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

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- Definition

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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- Definition

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

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- Definition

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

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- Definition

Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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- Definition

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

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- Definition

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

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