Terra Nova Working Interest Redetermination - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Commitments and Contingencies Disclosure [Line Items]
Redetermination of Terra Nova working interest	$ (5,351)	[1]	$ 18,582	[1],[2]	$ 83,498	[1],[2]
Joint Operating Agreement
Commitments and Contingencies Disclosure [Line Items]
Joint agreement ownership interest	12.00%
End of Period
Commitments and Contingencies Disclosure [Line Items]
Joint agreement ownership interest	10.475%

[1] Results exclude corporate overhead, interest and discontinued operations.

[2] Reclassified to conform to current presentation.