Commitments - Additional Information (Detail)	Sep. 30, 2012 ft3
Commitments and Contingencies Disclosure [Line Items]
Natural gas deliveries contract, cubic feet per day	50,000,000
Natural gas deliveries contract, average price per thousand cubic feet, in Canadian dollars	4.43

The delivery price committed to in the contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Industry Guide

-Number 2

-Paragraph 8

Name:	us-gaap_OilAndGasDeliveryCommitmentsAndContractsFixedPrice
Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	instant