Summary of Significant Accounting Policies - Additional Information 1 (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary Of Significant Accounting Policies [Line Items]
Net book value of unproved properties	[1]	$ 949,155				$ 943,246				$ 949,155	$ 943,246	$ 807,022
Abandonment and impairment of unproved properties		11,432	$ 12,366	$ 12,330	$ 11,491	14,308	$ 13,444	$ 9,332	$ 9,995	47,619	47,079	51,918
Depreciation expense										11,900	12,900	$ 13,200
Marketable securities held in deferred compensation plans		62,400				68,500				62,400	68,500
Surface acreage		$ 10,600				$ 10,300				$ 10,600	$ 10,300
Minimum | Other property and equipment
Summary Of Significant Accounting Policies [Line Items]
Useful life of assets										3 years
Maximum | Other property and equipment
Summary Of Significant Accounting Policies [Line Items]
Useful life of assets										10 years

[1] Includes capitalized asset retirement costs and the associated accumulated amortization.