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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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- Definition Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Exchanged Restricted Shares In Period Weighted Average Grant Date Fair Value. + References No definition available. + Details
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- Definition Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Exchanged Stock Appreciation Rights In Period Weighted Average Grant Date Fair Value. + References No definition available. + Details
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- Definition Share based compensation arrangement by share based payment award equity instruments exchanged stock appreciation rights vested prior to exchange in period weighted average grant date fair value. + References No definition available. + Details
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- Definition Share-based compensation arrangement by share-based payment award, equity instruments other than options, exchanged stock appreciation rights vested prior to exchange in period. + References No definition available. + Details
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- Definition 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). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued 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). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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