Concentrations - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Unusual Risk or Uncertainty [Line Items]
Maximum amount of credit risk exposure	$ 83,432
Production associated with Gulf Coast Basin properties	18.00%
Estimated reserves derived from reservoirs associated with deep water and deep shelf gas properties	38.00%
Gulf Coast Basin Conventional Shelf Properties
Unusual Risk or Uncertainty [Line Items]
Estimated proved reserves derived	56.00%
GOM Deep Water and Deep Shelf Gas Properties
Unusual Risk or Uncertainty [Line Items]
Estimated proved reserves derived	27.00%