Business Segment Information (Schedule Of Reconciliation Of Operating Profit (Loss) From Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Business Segment Information [Abstract]
Segment profits	$ 103,211	$ 128,504	$ 196,514	$ 262,073
General and administrative expenses	(49,321)	(45,540)	(91,278)	(86,898)
Depreciation and amortization	(52,067)	(45,536)	(101,848)	(89,520)
Loss on disposal of assets	(790)	(980)	(1,879)	(2,699)
Operating income	$ 1,033	$ 36,448	$ 1,509	$ 82,956