Segment Information (Reconciliation of Segment Profit to Operating Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting [Abstract]
Segment Profits	$ 262,876	$ 263,387	$ 233,240
General and administrative	(65,083)	(55,516)	(51,172)
(Gain) loss on derivatives	(1,006)	(7,776)	(9,100)
Gain on sale of property	342	(264)	13,881
Depreciation, amortization and impairments	(162,300)	(125,358)	(112,936)
Operating income	$ 34,829	$ 74,473	$ 73,913