Derivatives and Hedging-Disclosures and Fair Value Measurements - Offsetting of Financial Assets (Liabilities) and Derivative Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Net Assets (Liabilities) Presented in the Statement of Financial Position		$ (11,437)
Subject to an enforceable master netting arrangement
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Gross Assets Recognized	$ 14,956	26,164
Gross Liabilities Offset in the Statement of Financial Position	(8,777)	(37,490)
Net Assets (Liabilities) Presented in the Statement of Financial Position	6,179	(11,326)
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	6,179	(11,326)
Subject to an enforceable master netting arrangement \| Fair asset value of derivative instruments
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Gross Assets Recognized	13,514
Gross Liabilities Offset in the Statement of Financial Position	(8,317)
Net Assets (Liabilities) Presented in the Statement of Financial Position	5,197
Gross Amounts Not Offset in the Statement of Financial Position, Net Amount	5,197
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	1,442	1,605
Gross Liabilities Offset in the Statement of Financial Position	(460)	(1,478)
Net Assets (Liabilities) Presented in the Statement of Financial Position	982	127
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	$ 982	127
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		24,274
Gross Liabilities Offset in the Statement of Financial Position		(35,711)
Net Assets (Liabilities) Presented in the Statement of Financial Position		(11,437)
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		(11,437)
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		285
Gross Liabilities Offset in the Statement of Financial Position		(301)
Net Assets (Liabilities) Presented in the Statement of Financial Position		(16)
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		$ (16)

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