Selected Quarterly Financial Data (Narrative) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended			3 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Executive Officers [Member]	Sep. 30, 2013 Exploration and Production [Member]
Quarterly Financial Data [Line Items]
Relocation expenses				$ 750	$ 8,031
Relocation expenses, net of tax				463	4,975
Expense associated with cessation of the use of headquarters	(1,338)	10,498						742
Expense associated with cessation of the use of headquarters, net of tax	(826)	6,483						458
Equity-based compensation expense				15,397	17,289	11,879	3,585
Equity-based compensation expense, net of taxes				9,508	11,803	7,365	3,315
Gain from litigation settlement			3,551		3,551
Gain from litigation settlement, net of tax			$ 2,202