Offsetting of Financial Assets (Liabilities) and Derivative Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Net Assets (Liabilities) Presented in the Statement of Financial Position	$ 5,932	$ 3,987
Net Assets (Liabilities) Presented in the Statement of Financial Position	(289)	(2,285)
Net Amount		(40)
Subject to an enforceable master netting arrangement
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Gross Assets Recognized	8,725	13,061
Gross Liabilities Offset in the Statement of Financial Position	(2,817)	(10,555)
Net Assets (Liabilities) Presented in the Statement of Financial Position	5,908	2,506
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	5,908	2,506
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		481
Gross Liabilities Offset in the Statement of Financial Position	(1)	(484)
Net Assets (Liabilities) Presented in the Statement of Financial Position	(1)	(3)
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	(1)	(3)
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	1,706	3,976
Gross Liabilities Offset in the Statement of Financial Position	(1,995)	(6,261)
Net Assets (Liabilities) Presented in the Statement of Financial Position	(289)	(2,285)
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	(289)	(2,285)
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	6,023	7,716
Gross Liabilities Offset in the Statement of Financial Position	(91)	(3,729)
Net Assets (Liabilities) Presented in the Statement of Financial Position	5,932	3,987
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	5,932	3,987
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	996	888
Gross Liabilities Offset in the Statement of Financial Position	(730)	(81)
Net Assets (Liabilities) Presented in the Statement of Financial Position	266	807
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	$ 266	$ 807