Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Commitments and Contingencies Disclosure [Line Items]
Operating lease rental expense	$ 11,400,000	$ 14,800,000	$ 18,000,000
Asset retirement obligations	6,283,000	7,364,000	6,835,000
Environmental Compliance
Commitments and Contingencies Disclosure [Line Items]
Asset retirement obligations	6,283,000
Legal Reserve
Commitments and Contingencies Disclosure [Line Items]
Reserve established for contingency matters	200,000	900,000
Sales and Use Tax Audit
Commitments and Contingencies Disclosure [Line Items]
Reserve established for contingency matters	300,000	500,000
Drilling Commitments
Commitments and Contingencies Disclosure [Line Items]
Contract termination provisions	Early termination provisions that would require us to pay penalties if we terminate the agreements prior to the end of their original terms.
Penalty amount for termination	$ 14,100,000
Drilling Commitments | Maximum
Commitments and Contingencies Disclosure [Line Items]
Contract Term	3 years
Firm Transportation Commitments | Maximum
Commitments and Contingencies Disclosure [Line Items]
Contract Term	15 years
Firm Transportation Commitments | Minimum
Commitments and Contingencies Disclosure [Line Items]
Contract Term	1 year