Pension and Other Post-Retirement Benefit Plans (Funded Status) (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]
Change in benefit obligation [Roll Forward]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	7,284	8,775	14,568	17,550
Change in plan assets [Roll Forward]
Employer contributions			1,787
Post-Retirement Healthcare Plans [Member]
Change in benefit obligation [Roll Forward]
Service cost	30	39	60	78
Interest cost	$ 32	$ 36	$ 64	$ 72