WTI Open Contracts (Detail)	Dec. 31, 2013 bbl
January to March 2014 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of barrels	20,000
Natural gas deliveries contract average price per thousand cubic feet	98.47
April to June 2014 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of barrels	20,000
Natural gas deliveries contract average price per thousand cubic feet	96.48
July to September 2014 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of barrels	7,000
Natural gas deliveries contract average price per thousand cubic feet	95.24