Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commitments and Contingencies Disclosure [Line Items]
Operating lease rental expense	$ 11,000,000	$ 11,400,000	$ 14,800,000
Asset retirement obligations	4,513,000	6,283,000	7,364,000
Environmental Compliance
Commitments and Contingencies Disclosure [Line Items]
Asset retirement obligations	4,500,000
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
Contract Drilling
Commitments and Contingencies Disclosure [Line Items]
Contract termination claims description	early termination provisions that would require us to pay penalties if we terminate the agreements prior to the end of their original terms.
Loss on contract termination for default	$ 2,000,000
Maximum | Contract Drilling
Commitments and Contingencies Disclosure [Line Items]
Contract term	3 years
Maximum | Firm Transportation
Commitments and Contingencies Disclosure [Line Items]
Contract term	15 years
Minimum | Firm Transportation
Commitments and Contingencies Disclosure [Line Items]
Contract term	1 year