Acquisitions (Summary Of Fair Value Of Assets Acquired And Liabilities Assumed For East Texas Oil Field Acquisition) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 28, 2012		Dec. 31, 2011	Oct. 03, 2011	Dec. 04, 2012 East Texas Oil Field Properties [Member]
Business Acquisition [Line Items]
Evaluated	$ 1,656,146	$ 141,315		$ 1,076,828		$ 215,693
Unevaluated	11,500					5,400
Other assets						1,900
Asset retirement obligation		(34,261)			(26,294)	(9,843)
Other current liabilities						(1,190)
Net assets acquired		(45,578)			249,331	211,960
Estimated purchase price adjustment		5,270	[1]		2,715	2,346
Cash paid for acquisition						$ 214,306

[1] Represents a reclamation deposit in escrow as security for abandonment and redemption obligations.