CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Income	$ 98,406	$ 92,556	$ 77,376
Reclassification of net gains on derivative instruments	(732)	(730)	(1,188)
Reclassification of deferred tax liability on net gains on derivative instruments	0	(3,572)	0
Postretirement medical liability adjustment	(553)	(581)	(134)
Foreign currency translation	(54)	25	111
Total Other Comprehensive Loss	(1,339)	(4,858)	(1,211)
Comprehensive Income	$ 97,067	$ 87,698	$ 76,165