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Financial Instruments - Effect of Derivative Instruments on Condensed Consolidated Statement of Operations (Parenthetical) (Detail) (USD $)
In Thousands, unless otherwise specified
1 Months Ended 9 Months Ended
Jan. 31, 2014
Sep. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]    
Swaps, settlement dates description   January 2015 through December 2015
Net proceeds from derivative instruments $ 276 $ 703
Gains on settlement of derivative instruments   $ 979
Crude Oil Commodity Contracts [Member]
   
Derivative Instruments, Gain (Loss) [Line Items]    
Swaps, settlement dates description   January 2016 through December 2016