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Share-Based Compensation - Schedule of Restricted Stock Activity (Detail) - Restricted Stock [Member] - $ / shares		1 Months Ended			12 Months Ended
	Aug. 14, 2018	Apr. 30, 2019	Aug. 31, 2018	Jul. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
2011 and 2017 Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested, Beginning Balance						0	775,753
Number of Shares, Granted							0
Number of Shares, Vested							(284,555)
Number of Shares, Cancelled							(491,198)
Number of Shares, Unvested, Ending Balance							0
Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance						$ 0	$ 5.22
Weighted-Average Grant Date Fair Value, Granted							0
Weighted-Average Grant Date Fair Value, Vested							5.26
Weighted-Average Grant Date Fair Value, Cancelled							5.20
Weighted-Average Grant Date Fair Value, Unvested, Ending Balance							$ 0
2018 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested, Beginning Balance					847,974	1,250,625	0
Number of Shares, Granted	1,266,034	3,481,370			910,297	321,926
Exchanged Restricted Shares							491,198
Exchanged Phantom Stock							491,915
Exchanged SARs							1,266,034
Exchanged SARs vested prior to exchange							(966,022)
Number of Shares, Vested		(2,255,577)			(555,473)	(701,582)	(32,500)
Number of Shares, Cancelled		(30,245)	(966,022)	(491,915)	(7,250)	(22,995)	0
Number of Shares, Unvested, Ending Balance					1,195,548	847,974	1,250,625
Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance					$ 9.56	$ 9.59	$ 0
Weighted-Average Grant Date Fair Value, Granted					3.97	8.94
Exchanged Restricted Shares							5.20
Exchanged Phantom Stock							12.00
Exchanged SARs							12.00
Exchanged SARs vested prior to exchange							12.00
Weighted-Average Grant Date Fair Value, Vested					9.21	9.25	2.00
Weighted-Average Grant Date Fair Value, Cancelled					7.89	12.00	0
Weighted-Average Grant Date Fair Value, Unvested, Ending Balance					$ 5.47	$ 9.56	$ 9.59

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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