Pension and Other Postretirement Benefits (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Pension Benefits [Member]
Components of net periodic benefit cost :
Service cost	$ 5,863	$ 4,994	$ 4,949
Interest cost	11,687	11,508	12,163
Expected return on plan assets	(11,170)	(11,436)	(11,455)
Amortization of prior service cost	(63)	(129)	20
Special termination benefits		13
Net loss recognition	6,030	4,775	2,293
Net periodic benefit cost	12,347	9,725	7,970
Other Benefits [Member]
Components of net periodic benefit cost :
Service cost	92	142	91
Interest cost	2,199	2,305	2,330
Amortization of prior service cost	(116)	(195)	(203)
Net loss recognition	386	424	248
Net periodic benefit cost	$ 2,561	$ 2,676	$ 2,466