Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segment Reporting [Abstract]
Segment Profits	$ 59,733	$ 68,645	$ 131,679	$ 133,437
General and administrative	(13,774)	(13,272)	(29,380)	(25,754)
Gain (loss) on derivatives	4,905	(1,536)	2,736	(4,957)
Gain on sale of property	406	60	504	80
Depreciation, amortization, and impairments	(32,889)	(31,654)	(65,085)	(61,326)
Operating Income Loss	$ 18,381	$ 22,243	$ 40,454	$ 41,480