Pension Plans And Other Post-Retirement Benefits (Schedule Of Changes In Benefit Obligation And Fair Value Of Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member]
Change in benefit obligation:
Benefit obligation at January 1	$ 281,964	$ 320,979
Service cost	2,718	3,249	$ 3,174
Interest cost	11,817	11,495	12,434
Actuarial (gain)/loss	36,885	(23,080)
Plan participants' contributions
Benefits paid	(23,003)	(30,679)
Benefit obligation at December 31	310,381	281,964	320,979
Change in plan assets:
Fair value of plan assets at January 1	239,007	270,353
Actual return on plan assets	41,955	(16,852)
Employer contributions	8,502	16,185
Benefits paid	(23,003)	(30,679)
Fair value of plan assets at December 31	266,461	239,007	270,353
Funded status of plan:
Net liability recognized at December 31,	43,920	42,957
Other Postretirement Benefits [Member]
Change in benefit obligation:
Benefit obligation at January 1	69,443	75,960
Service cost	819	1,049	1,020
Interest cost	2,999	2,831	2,947
Actuarial (gain)/loss	7,238	(8,970)
Plan participants' contributions	145	127
Benefits paid	(1,102)	(1,554)
Benefit obligation at December 31	79,542	69,443	75,960
Change in plan assets:
Fair value of plan assets at January 1	45,422	47,750
Actual return on plan assets	9,436	(2,599)
Employer contributions		1,636
Benefits paid	(847)	(1,365)
Fair value of plan assets at December 31	54,011	45,422	$ 47,750
Funded status of plan:
Net liability recognized at December 31,	$ 25,531	$ 24,021