Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension
Components of net periodic benefit cost:
Service cost		$ 3,728		$ 11,852
Interest cost	3,589	4,790	10,769	14,345
Expected return on assets	(3,874)	(5,159)	(11,622)	(15,530)
Amortization of net loss	12	23	35	296
Net periodic benefit cost	(273)	3,382	(818)	10,963
Postretirement
Components of net periodic benefit cost:
Service cost	81	76	242	234
Interest cost	64	71	193	214
Curtailment gain				(110)
Net periodic benefit cost	$ 145	$ 147	$ 435	$ 338