Derivative Financial Instruments - Summary of Gain (Loss) Recognized in Income on Oil and Gas Commodity Contracts on (Detail)	6 Months Ended
Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Document Period End Date	Mar. 31, 2014

The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

No definition available.

Name:	dei_DocumentPeriodEndDate
Namespace Prefix:	dei_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration