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Leases - Additional Information (Detail) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Mar. 31, 2022 USD ($) Air-craft | Mar. 31, 2021 USD ($) | Mar. 31, 2022 USD ($) Air-craft | Mar. 31, 2021 USD ($)
Leases [Abstract] |  |  |  |
Number of leased aircraft | Air-craft | 18 |  | 18 |
Aggregate rental expense under all operating aircraft, equipment and facility leases | $ 11.0 | $ 11.3 | $ 22.2 | $ 22.7
Weighted average remaining lease term Operating leases | 3 years 8 months 12 days |  | 3 years 8 months 12 days |
Weighted average discount rate Operating leases | 4.40% |  | 4.40% |
Impairment of certain operating lease ROU assets | $ 0.4 |  | $ 0.4 |

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- Definition Amount of loss from impairment of right-of-use asset from operating lease. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 25 -Paragraph 6 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123399704&loc=SL77918431-209957 + Details
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- Definition Weighted average remaining lease term for operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 55 -Paragraph 53 -URI http://asc.fasb.org/extlink&oid=123414884&loc=SL77918982-209971 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(3) -URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980 + Details
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- Definition Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=123406913&loc=d3e41499-112717 + Details
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