Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2010
Commitments and Contingencies Disclosure [Line Items]
Operating lease rental expense	$ 8,700,000	$ 9,400,000	$ 11,000,000
Asset retirement obligations	5,890,000	6,437,000	4,513,000
Environmental Compliance
Commitments and Contingencies Disclosure [Line Items]
Asset retirement obligations	5,900,000
Legal Reserve
Commitments and Contingencies Disclosure [Line Items]
Reserve established for contingency matters				900,000
Contract Drilling
Commitments and Contingencies Disclosure [Line Items]
Contract termination claims description	early termination provisions that require us to pay liquidated damages if we terminate the agreements prior to the end of their original terms.
Penalty incurred if agreement terminated as of end of period	$ 17,200,000
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