Pension and Other Postretirement Benefits (Details 11) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Pension and other postretirement benefits expenses
Service cost	$ 5,961	$ 6,055	$ 5,395
Interest cost	17,383	18,819	19,494
Expected return on plan assets	(29,900)	(28,082)	(30,302)
Amortization of prior service cost	560	446	210
Recognized losses	11,628	10,557	10,791
Curtailment loss gain	0	(7,217)	0
Settlement loss	0	(119)	0
Net periodic benefit cost	5,632	459	5,588
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	8,618
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	404
Other postretirement benefit plans [Member]
Pension and other postretirement benefits expenses
Service cost	85	83	122
Interest cost	1,358	1,561	1,766
Expected return on plan assets	0	0	0
Amortization of prior service cost	20	(68)	(373)
Recognized losses	561	276	535
Curtailment loss gain	0	0	0
Settlement loss	0	0	0
Net periodic benefit cost	2,024	$ 1,852	$ 2,050
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	40
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	$ 25