Oil and Gas Reserves Information (Unaudited) - Changes in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Reserves (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reserve Quantities [Line Items]
Standardized Measure, Beginning of Year	$ 641,325	$ 887,798	$ 606,136
Net change in sales price, net of production costs	43,117	(217,925)	506
Development costs incurred during the year which were previously estimated	187,643	179,549	205,418
Revisions of quantity estimates	48,411	(886,531)	(50,399)
Accretion of discount	81,434	117,381	79,763
Changes in future development and abandonment costs	(157,207)	628,088	10,962
Changes in timing and other	80,348	27,077	(58,304)
Extensions and discoveries	291,582	337,223	540,937
Purchases of minerals in place			2,959
Sales of minerals in place		(236,925)
Sales, net of production costs	(335,677)	(307,407)	(355,654)
Net changes in income taxes	(73,759)	112,997	(94,526)
Standardized Measure, End of Year	$ 807,217	$ 641,325	$ 887,798