Pension Plans and Other Postretirement Benefits (Details-2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Components of Net Periodic Cost (Benefit)
Service cost	$ 5,365	$ 7,263	$ 6,179
Interest cost	12,393	13,766	13,574
Expected return on assets	(22,365)	(22,682)	(22,051)
Amortization of:
Transition obligation	0	0	0
Prior service cost (benefit)	10	23	204
Actuarial loss	5,600	5,395	703
Net periodic cost (benefit)	1,003	3,765	(1,391)
Postretirement Benefits [Member]
Components of Net Periodic Cost (Benefit)
Service cost	1,271	1,559	1,339
Interest cost	2,681	3,075	3,166
Expected return on assets	(2,829)	(2,812)	(2,615)
Amortization of:
Transition obligation	3	3	3
Prior service cost (benefit)	(2,669)	(2,669)	(2,669)
Actuarial loss	589	953	252
Net periodic cost (benefit)	$ (954)	$ 109	$ (524)