Equity Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Prior service cost	$ (645)		$ (645)		$ (734)
Transition asset	210		210		259
Unrecognized net actuarial loss	(1,264)		(1,264)		(1,264)
Net income	54,549	45,109	161,430	131,485
Amortization of deferred pension costs, net of tax			40
Total accumulated other comprehensive income (loss)	$ (1,699)		$ (1,699)		$ (1,739)