Pension and Other Post-Retirement Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Plans [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	7,284	8,775	14,568	17,550
Expected return on plan assets	(10,523)	(10,930)	(21,046)	(21,859)
Amortization of prior service cost	0	0	0	0
Amortization of net (gain) loss	887	1,937	1,774	3,874
Net periodic benefit cost (income)	(2,352)	(218)	(4,704)	(435)
Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	30	39	60	78
Interest cost	32	36	64	72
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	(13)	0	(26)
Amortization of net (gain) loss	55	71	110	142
Net periodic benefit cost (income)	$ 117	$ 133	$ 234	$ 266