Equity Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Prior service cost	$ (674)		$ (674)		$ (734)
Transition asset	226		226		259
Unrecognized net actuarial loss	(1,264)		(1,264)		(1,264)
Net income	52,951	40,384	106,881	86,376
Amortization of deferred pension costs, net of tax			27
Total accumulated other comprehensive income (loss)	$ (1,712)		$ (1,712)		$ (1,739)