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Derivatives and Hedging-Disclosures and Fair Value Measurements - Offsetting of Financial Assets (Liabilities) and Derivative Assets (Liabilities) (Detail) - USD ($) $ in Thousands | Jun. 30, 2019 | Sep. 30, 2018
--- | --- | ---
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items] |  |
Net Assets (Liabilities) Presented in the Statement of Financial Position |  | $ 17,710
Net Assets (Liabilities) Presented in the Statement of Financial Position | $ (2,418) |
Subject to an enforceable master netting arrangement |  |
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items] |  |
Gross Assets Recognized | 11,368 | 18,616
Gross Liabilities Offset in the Statement of Financial Position | (13,823) | (103)
Net Assets (Liabilities) Presented in the Statement of Financial Position | (2,455) | 18,513
Financial Instruments |  | 0
Cash Collateral Received |  | 0
Net Amount | (2,455) | 18,513
Subject to an enforceable master netting arrangement | Fair asset and fair liability value of derivative instruments |  |
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items] |  |
Gross Assets Recognized |  | 17,710
Net Assets (Liabilities) Presented in the Statement of Financial Position |  | 17,710
Financial Instruments |  | 0
Cash Collateral Received |  | 0
Net Amount |  | 17,710
Subject to an enforceable master netting arrangement | Deferred charges and other assets, net |  |
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items] |  |
Gross Assets Recognized | 112 |
Gross Liabilities Offset in the Statement of Financial Position | (92) |
Net Assets (Liabilities) Presented in the Statement of Financial Position | 20 |
Net Amount | 20 |
Subject to an enforceable master netting arrangement | Other long-term assets, net |  |
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items] |  |
Gross Assets Recognized |  | 906
Gross Liabilities Offset in the Statement of Financial Position |  | (103)
Net Assets (Liabilities) Presented in the Statement of Financial Position |  | 803
Financial Instruments |  | 0
Cash Collateral Received |  | 0
Net Amount |  | 803
Subject to an enforceable master netting arrangement | Fair liability and fair asset value of derivative instruments |  |
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items] |  |
Gross Assets Recognized | 10,299 |
Gross Liabilities Offset in the Statement of Financial Position | (12,717) |
Net Assets (Liabilities) Presented in the Statement of Financial Position | (2,418) |
Financial Instruments |  | 0
Cash Collateral Received |  | 0
Net Amount | (2,418) |
Subject to an enforceable master netting arrangement | Other long-term liabilities |  |
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items] |  |
Gross Assets Recognized | 957 |
Gross Liabilities Offset in the Statement of Financial Position | (1,014) |
Net Assets (Liabilities) Presented in the Statement of Financial Position | (57) |
Financial Instruments |  | 0
Cash Collateral Received |  | $ 0
Net Amount | $ (57) |

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