Pension Plans and Other Postretirement Benefits (Details-2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	$ 5,723	$ 5,383	$ 5,365
Interest cost	12,859	12,625	12,393
Expected return on assets	(26,241)	(22,963)	(22,365)
Amortization of:
Transition obligation	0	0	0
Prior service (credit) cost	(44)	(17)	10
Actuarial loss	5,278	6,352	5,600
Net periodic benefit cost (credit)	(2,425)	1,380	1,003
Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	1,283	1,231	1,271
Interest cost	2,612	2,666	2,681
Expected return on assets	(3,232)	(2,887)	(2,829)
Amortization of:
Transition obligation	3	3	3
Prior service (credit) cost	(2,669)	(2,669)	(2,669)
Actuarial loss	488	660	589
Net periodic benefit cost (credit)	$ (1,515)	$ (996)	$ (954)