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Share-Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands |  |  |  | 1 Months Ended | 12 Months Ended | 72 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 11, 2018 | Aug. 14, 2018 | Oct. 17, 2017 | Apr. 30, 2019 | Aug. 31, 2018 | Jul. 31, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2014 | Sep. 30, 2019 | Apr. 09, 2019 | Sep. 30, 2016
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 |  |  |  |  |  |  | $ 5,900 |  |  |  | $ 5,900 |  |
Unrecognized compensation cost, period for recognition |  |  |  |  |  |  | 1 year 6 months |  |  |  |  |  |
Share-based compensation expense |  |  |  |  |  |  | $ 5,500 | $ 12,900 | $ 2,300 |  |  |  |
Repurchased shares, value |  |  |  |  |  |  | $ 1,872 | $ 7,709 | $ 1,043 |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Stock issued during period, shares, new issues |  |  |  |  |  |  |  | 10,354,018 |  |  |  |  |
Repurchased shares, shares |  |  |  |  |  |  | 205,235 | 438,541 |  |  |  |  |
Repurchased shares, value |  |  |  |  |  |  | $ 1,900 | $ 5,000 |  |  |  |  |
IPO [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Stock issued during period, shares, new issues |  | 9,630,000 |  |  |  |  |  |  |  |  |  |  |
Board of Directors [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Shares vesting period |  |  |  |  |  |  | 1 year |  |  |  |  |  |
Stock Appreciation Rights [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares vested |  |  |  |  |  |  |  | 622,238 | 1,460,812 |  | 3,687,218 |  |
Number of shares cancelled |  |  |  |  |  |  |  | 517,775 |  |  |  |  |
Number of shares unvested |  |  |  |  |  |  |  | 0 | 1,140,013 |  |  |  | 2,223,333
Number of shares granted |  |  |  |  |  |  |  | 0 | 384,160 |  | 4,204,993 |  |
Number of shares authorized |  |  |  |  |  |  |  |  |  | 5,000,000 |  |  |
Shares vesting period |  |  |  |  |  |  |  |  |  | 3 years |  |  |
Shares expiration period |  |  |  |  |  |  |  |  |  | 10 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 granted |  |  |  |  |  |  |  |  |  |  | 536,538 |  |
Number of shares authorized |  |  | 1,250,000 |  |  |  |  |  |  |  |  |  |
Shares vesting period |  |  | 3 years |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |
Restricted Stock Award | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Shares vesting period |  |  |  |  |  |  | 3 years |  |  |  |  |  |
Restricted Stock Award | 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 |
2018 Equity Incentive Plan [Member] | Restricted Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares vested |  |  |  | 1,700,104 |  |  | 701,582 | 32,500 | 0 |  |  |  |
Stock issued during period, shares, new issues |  |  |  |  |  | 2,249,147 |  |  |  |  |  |  |
Number of shares cancelled |  |  |  | 22,995 | 966,022 | 491,915 | 22,995 | 0 |  |  |  |  |
Unvested restricted shares issued |  |  |  |  |  | 491,198 |  |  |  |  |  |  |
Number of shares unvested |  |  |  |  |  |  | 847,974 | 1,250,625 | 0 |  | 847,974 |  | 0
Number of shares granted |  | 1,266,034 |  | 2,571,073 |  |  | 321,926 |  | 0 |  |  |  |
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 |  |  |  |  | 1,598,885 | 966,022 |  |  |  |  |  |  |
Stock issued during period, shares, new issues |  |  |  |  |  | 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 Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition. + 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=116856206&loc=d3e5070-113901 + Details
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