Commitments - Additional Information (Detail)	Sep. 30, 2011 cf
Fiscal Year 2011
Commitments and Contingencies Disclosure [Line Items]
Natural gas deliveries contract, million cubic feet per day	99,000,000
Natural gas deliveries contract, price per thousand cubic feet, in Canadian dollars	4.90
Fiscal Year 2012
Commitments and Contingencies Disclosure [Line Items]
Natural gas deliveries contract, million cubic feet per day	50,000,000
Natural gas deliveries contract, price per thousand cubic feet, in Canadian dollars	4.43