Business Segment Information (Schedule Of Reconciliation Of Operating Profit (Loss) From Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Business Segment Information [Abstract]
Segment profits	$ 133,569	$ 89,968
General and administrative expenses	(41,358)	(31,341)
Depreciation and amortization	(43,984)	(32,980)
Gain (loss) on disposal of assets	(1,719)	1,705
Operating income	$ 46,508	$ 27,352