Pension and Other Postretirement Benefits (Details 11) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined benefit pension plans [Member]
Pension and other postretirement benefits expenses
Service cost	$ 5,395	$ 5,508	$ 4,546
Interest cost	19,494	20,019	22,026
Expected return on plan assets	(30,302)	(32,404)	(34,232)
Amortization of prior service cost	210	305	648
Recognized losses	10,791	15,004	8,617
Curtailment loss gain	0	0	219
Settlement loss	0	9,939	871
Special termination benefit	0	0	715
Net periodic benefit cost	5,588	18,371	3,410
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 2017	9,997
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 2017	441
Other postretirement benefit plans [Member]
Pension and other postretirement benefits expenses
Service cost	122	145	139
Interest cost	1,766	1,836	2,179
Expected return on plan assets	0	0	0
Amortization of prior service cost	(373)	(564)	(871)
Recognized losses	535	1,011	1,017
Curtailment loss gain	0	0	4
Settlement loss	0	0	0
Special termination benefit	0	0	0
Net periodic benefit cost	2,050	$ 2,428	$ 2,468
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 2017	276
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 2017	$ (68)