Future Net Cash Flows Relating to Proved Oil and Gas Reserves (Parenthetical) (Detail)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]      
Discount factor 10.00% 10.00% 10.00%