Income Taxes - Provision (Benefit) for Income Taxes (Parenthetical) (Detail)	1 Months Ended
	Jul. 31, 2011 Petroleum Operations [Member]	Jul. 31, 2012 Dismantlement Expenses [Member]
Income Tax Expense Benefit [Line Items]
Old supplementary tax rate (in percentage)	20.00%	32.00%
New supplementary tax rate (in percentage)	32.00%	20.00%