Pension Plans and Other Postretirement Benefits (Details-2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of Net Periodic Cost (Benefit)
Transition obligation straight-line amortization period	20 years
Pension Benefits [Member]
Components of Net Periodic Cost (Benefit)
Service cost	$ 7,263	$ 6,179	$ 7,705
Interest cost	13,766	13,574	12,656
Expected return on assets	(22,682)	(22,051)	(19,027)
Amortization of:
Transition obligation	0	0	0
Prior service cost (benefit)	23	204	314
Actuarial loss	5,395	703	8,014
Net periodic cost (benefit)	3,765	(1,391)	9,662
Postretirement Benefits [Member]
Components of Net Periodic Cost (Benefit)
Service cost	1,559	1,339	2,380
Interest cost	3,075	3,166	3,871
Expected return on assets	(2,812)	(2,615)	(2,176)
Amortization of:
Transition obligation	3	3	3
Prior service cost (benefit)	(2,669)	(2,669)	110
Actuarial loss	953	252	1,236
Net periodic cost (benefit)	$ 109	$ (524)	$ 5,424