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Share-Based Compensation - Additional Information (Detail) - USD ($) $ in Millions |  |  |  | 1 Months Ended | 12 Months Ended | 60 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 11, 2018 | Aug. 14, 2018 | Oct. 17, 2017 | Aug. 31, 2018 | Jul. 31, 2018 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2014 | Sep. 30, 2018 | Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
IPO issuance, shares | 1,344,500 |  |  |  |  |  |  |  |  |  |
Unrecognized compensation cost related to unvested share-based compensation arrangements |  |  |  |  |  | $ 8.8 |  |  |  | $ 8.8 |
Unrecognized compensation cost, period for recognition |  |  |  |  |  | 1 year 6 months |  |  |  |  |
Share-based compensation expense |  |  |  |  |  | $ 12.9 | $ 2.3 | $ 4.7 |  |  |
IPO [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
IPO issuance, shares |  | 9,630,000 |  |  |  |  |  |  |  |  |
Stock Appreciation Rights [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of shares vested |  |  |  |  |  | 622,238 | 1,460,812 | 776,667 |  | 3,687,218 |
Number of shares authorized |  |  |  |  |  |  |  |  | 5,000,000 |  |
Number of shares cancelled |  |  |  |  |  | 517,775 |  |  |  |  |
Number of shares unvested |  |  |  |  |  | 0 | 1,140,013 | 2,223,333 |  | 0 | 2,372,500
Number of shares granted |  |  |  |  |  | 0 | 384,160 | 827,500 |  | 4,204,993 |
Shares expiration period |  |  |  |  |  |  |  |  | 10 years |  |
Shares vesting period |  |  |  |  |  |  |  |  | 3 years |  |
Number of shares exercised |  |  |  |  |  |  |  |  |  | 2,088,333 |
Restricted Stock Units [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of shares vested |  |  |  |  |  |  |  |  |  | 44,623 |
Number of shares authorized |  |  | 1,250,000 |  |  |  |  |  |  |  |
Number of shares granted |  |  |  |  |  |  |  |  |  | 536,538 |
Shares vesting period |  |  | 3 years |  |  |  |  |  |  |  |
2018 Equity Incentive Plan [Member] | Restricted Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of shares vested |  |  |  |  | 998,522 | 32,500 | 0 |  |  |  |
Number of shares authorized |  |  |  |  | 2,500,000 |  |  |  |  |  |
IPO issuance, shares |  |  |  |  | 2,249,147 |  |  |  |  |  |
Number of shares cancelled |  |  |  | 966,022 | 491,915 | 0 |  |  |  |  |
Unvested restricted shares issued |  |  |  |  | 491,198 |  |  |  |  |  |
Number of shares unvested |  |  |  |  |  | 1,250,625 | 0 | 0 |  | 1,250,625 |
Number of shares granted |  | 1,266,034 |  |  | 2,249,147 |  | 0 |  |  |  |
2018 Equity Incentive Plan [Member] | Stock Appreciation Rights [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of shares vested |  |  |  | 1,598,885 | 966,022 |  |  |  |  |  |
IPO issuance, shares |  |  |  |  | 1,266,034 |  |  |  |  |  |
Number of shares cancelled |  |  |  | 300,012 |  |  |  |  |  |  |
Number of shares unvested |  |  |  |  | 300,012 |  |  |  |  |  |
2018 Equity Incentive Plan [Member] | Stock Appreciation Rights [Member] | IPO [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unvested restricted shares issued |  |  |  | 517,775 |  |  |  |  |  |  |
2018 Equity Incentive Plan [Member] | Restricted Stock Units [Member] | IPO [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of shares cancelled |  |  |  | 491,915 |  |  |  |  |  |  |
2011 Plan [Member] | Restricted Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of shares vested |  |  |  |  | 1,978,550 |  |  |  |  |  |
Number of shares cancelled |  |  |  |  | 470,355 |  |  |  |  |  |
Number of shares granted |  |  |  |  | 2,448,905 |  |  |  |  |  |
2017 Plan [Member] | Restricted Stock [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of shares vested |  |  |  |  | 10,412 |  |  |  |  |  |
Number of shares cancelled |  |  |  |  | 20,843 |  |  |  |  |  |
Number of shares granted |  |  |  |  | 31,255 |  |  |  |  |  |

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- Definition Share based compensation arrangement by share based payment award equity instruments other than options exercised in period. + References No definition available. + Details
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- Definition Share based compensation arrangement by share based payment award equity instruments other than options issued in period. + References No definition available. + Details
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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition 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. + 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 (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation. + 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 (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (a)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + 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=109197908&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=109197908&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=109197908&loc=d3e5070-113901 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + 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 (a)(3) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (a)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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