Offsetting of Financial Assets (Liabilities) and Derivative Assets (liabilities) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Net Assets (Liabilities) Presented in the Statement of Financial Position	$ 2,342	$ 646
Net Assets (Liabilities) Presented in the Statement of Financial Position	(12,358)	(3,999)
Subject to an enforceable master netting arrangement
Fair Values Of Financial Assets And Liabilities Including Derivative Financial Instruments [Line Items]
Gross Assets Recognized	26,263	14,467
Gross Liabilities Offset in the Statement of Financial Position	(36,279)	(17,820)
Net Assets (Liabilities) Presented in the Statement of Financial Position	(10,016)	(3,353)
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	(10,016)	(3,353)
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	23,921	7,213
Gross Liabilities Offset in the Statement of Financial Position	(36,279)	(11,212)
Net Assets (Liabilities) Presented in the Statement of Financial Position	(12,358)	(3,999)
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	(12,358)	(3,999)
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	2,342	7,254
Gross Liabilities Offset in the Statement of Financial Position		(6,608)
Net Assets (Liabilities) Presented in the Statement of Financial Position	2,342	646
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	$ 2,342	$ 646