Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension
Components of net periodic benefit cost:
Service cost		$ 4,397
Interest cost	3,590	4,764
Expected return on assets	(3,874)	(5,212)
Amortization of net loss	12	249
Net periodic benefit cost	(272)	4,198
Postretirement
Components of net periodic benefit cost:
Service cost	81	81
Interest cost	64	72
Curtailment gain		(110)
Net periodic benefit cost	$ 145	$ 43