Pension and Other Postretirement Benefits (Details 11) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined benefit pension plans [Member]
Pension and other postretirement benefits expenses
Service cost	$ 4,546	$ 6,181	$ 6,530
Interest cost	22,026	20,112	21,624
Expected return on plan assets	(34,232)	(33,144)	(32,827)
Amortization of prior service cost	648	752	845
Recognized losses	8,617	16,365	12,048
Curtailment loss gain	219	199	0
Settlement loss	871	637	92
Special termination benefit	715	1,016	0
Net periodic benefit cost	3,410	12,118	8,312
Estimated net actuarial loss for the defined benefit pension plans that will be amortized from accumulated other non-owner changes to equity into net periodic benefit cost in 2013	14,640
Estimated prior service cost for the defined benefit pension plans that will be amortized from accumulated other non-owner changes to equity into net periodic benefit cost (credit) in 2013	313
Other postretirement benefit plans [Member]
Pension and other postretirement benefits expenses
Service cost	139	233	273
Interest cost	2,179	2,061	2,532
Expected return on plan assets	0	0	0
Amortization of prior service cost	(871)	(1,006)	(1,585)
Recognized losses	1,017	1,004	1,082
Curtailment loss gain	4	(3,081)	0
Settlement loss	0	0	0
Special termination benefit	0	0	0
Net periodic benefit cost	2,468	(789)	2,302
Estimated net actuarial loss for the defined benefit pension plans that will be amortized from accumulated other non-owner changes to equity into net periodic benefit cost in 2013	1,043
Estimated prior service cost for the defined benefit pension plans that will be amortized from accumulated other non-owner changes to equity into net periodic benefit cost (credit) in 2013	$ (564)