Derivatives and Hedging-Disclosures and Fair Value Measurements - Offsetting of Financial Assets (Liabilities) and Derivative Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Sep. 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	$ (8,262)
Subject to an enforceable master netting arrangement
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Gross Assets Recognized	15,290	18,616
Gross Liabilities Offset in the Statement of Financial Position	(23,805)	(103)
Net Assets (Liabilities) Presented in the Statement of Financial Position	(8,515)	18,513
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received		0
Gross Amounts Not Offset in the Statement of Financial Position, Net Amount	(8,515)	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
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received		0
Gross Amounts Not Offset in the Statement of Financial Position, Net Amount		17,710
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	16	906
Gross Liabilities Offset in the Statement of Financial Position	(16)	(103)
Net Assets (Liabilities) Presented in the Statement of Financial Position		803
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received		0
Gross Amounts Not Offset in the Statement of Financial Position, 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	13,824
Gross Liabilities Offset in the Statement of Financial Position	(22,086)
Net Assets (Liabilities) Presented in the Statement of Financial Position	(8,262)
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received		0
Gross Amounts Not Offset in the Statement of Financial Position, Net Amount	(8,262)
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	1,450
Gross Liabilities Offset in the Statement of Financial Position	(1,703)
Net Assets (Liabilities) Presented in the Statement of Financial Position	(253)
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments		0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received		$ 0
Gross Amounts Not Offset in the Statement of Financial Position, Net Amount	$ (253)

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