Pension and Other Postretirement Benefits (Details 11) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined benefit pension plans [Member]
Pension and other postretirement benefits expenses
Service cost	$ 5,508	$ 4,546	$ 6,181
Interest cost	20,019	22,026	20,112
Expected return on plan assets	(32,404)	(34,232)	(33,144)
Amortization of prior service cost	305	648	752
Recognized losses	15,004	8,617	16,365
Curtailment loss gain	0	219	199
Settlement loss	9,939	871	637
Special termination benefit	0	715	1,016
Net periodic benefit cost	18,371	3,410	12,118
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	10,218
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	207
Other postretirement benefit plans [Member]
Pension and other postretirement benefits expenses
Service cost	145	139	233
Interest cost	1,836	2,179	2,061
Expected return on plan assets	0	0	0
Amortization of prior service cost	(564)	(871)	(1,006)
Recognized losses	1,011	1,017	1,004
Curtailment loss gain	0	4	(3,081)
Settlement loss	0	0	0
Special termination benefit	0	0	0
Net periodic benefit cost	2,428	$ 2,468	$ (789)
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	704
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	$ (373)