Summary of Significant Accounting Policies - Additional Information 1 (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary Of Significant Accounting Policies [Line Items]
Net book value of unproved properties	$ 807,000,000				$ 743,500,000				$ 807,000,000	$ 743,500,000
Abandonment and impairment of unproved properties	5,852,000	11,692,000	19,156,000	15,218,000	21,230,000	40,118,000	43,641,000	20,289,000	51,918,000	125,278,000	79,703,000
Depreciation expense									13,200,000	13,200,000	16,200,000
Unamortized debt issuance costs	44,500,000				43,100,000				44,500,000	43,100,000
Marketable securities	67,766,000				57,776,000				67,766,000	57,776,000
Other investments	$ 9,000,000				$ 14,300,000				$ 9,000,000	$ 14,300,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Useful life of assets									10 years
Minimum | Associated assets
Summary Of Significant Accounting Policies [Line Items]
Useful life of assets									5 years
Minimum | Other property and equipment
Summary Of Significant Accounting Policies [Line Items]
Useful life of assets									3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Useful life of assets									15 years
Maximum | Associated assets
Summary Of Significant Accounting Policies [Line Items]
Useful life of assets									7 years
Maximum | Other property and equipment
Summary Of Significant Accounting Policies [Line Items]
Useful life of assets									15 years