Equity Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Prior service cost	$ (586)		$ (616)
Transition asset	179		195
Unrecognized net actuarial loss	(7,905)		(7,992)
Net income	56,732	53,930
Amortization of deferred pension costs, net of tax	101
Total accumulated other comprehensive income (loss)	$ (8,312)		$ (8,413)