Pension and Other Post-Retirement Benefit Plans (Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 10,833	$ 5,414
Estimated future employer contributions	1,700
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2017	38,035
2018	41,229
2019	43,907
2020	45,804
2021	47,565
Years 2022 to 2026	242,354
Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	362	$ 365
Estimated future employer contributions	400
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2017	415
2018	462
2019	512
2020	499
2021	467
Years 2022 to 2026	$ 1,390