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Share-Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands			1 Months Ended		12 Months Ended
	Sep. 11, 2018	Aug. 14, 2018	Apr. 30, 2019	Jul. 31, 2018	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Apr. 09, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period, shares, new issues	1,344,500
Unrecognized compensation cost related to unvested share-based compensation arrangements					$ 5,100
Unrecognized compensation cost, period for recognition					1 year 10 months 24 days
Share-based compensation expense					$ 3,100	$ 4,400	$ 5,500
Repurchased shares, value					$ 1,486	$ 586	$ 1,872
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchased shares, shares					155,174	142,439	205,235
Repurchased shares, value					$ 1,500	$ 600	$ 1,900
Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vesting period					1 year
Restricted Stock Units [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vesting period					3 years
Restricted Stock Units [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vesting period					5 years
2018 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized								3,500,000
Percentage of number of shares issued and outstanding				1.00%
2018 Equity Incentive Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested			2,748,042		492,465	555,473	701,582
Stock issued during period, shares, new issues				2,249,147
Number of shares cancelled			73,245	491,915	43,000	7,250	22,995
Unvested restricted shares issued				491,198
Number of shares unvested					1,006,206	1,195,548	847,974		1,250,625
Number of shares awarded		1,266,034	3,827,493		346,123	910,297	321,926
2018 Equity Incentive Plan [Member] | Restricted Stock [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized			2,500,000
2018 Equity Incentive Plan [Member] | Restricted Stock [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized			3,500,000
2018 Equity Incentive Plan [Member] | Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested				966,022
Stock issued during period, shares, new issues				1,266,034
Number of shares unvested				300,012

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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