Employee Benefit Plans and Other Postretirement Benefits (Schedule Of Obligation And Funded Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in plan assets:
Prepaid benefit costs (long-term assets)	$ 19,816	$ 0
Pension and SERPA Benefits
Change in benefit obligation:
Benefit obligation, beginning of period	1,986,435	2,009,000
Service cost	31,584	33,437	$ 40,039
Interest cost	85,076	90,827	87,345
Actuarial losses (gains)	195,444	13,481
Plan participant contributions	0	0
Plan amendments	(13,227)	0
Benefits paid	(84,291)	(160,310)
Benefit obligation, end of period	2,201,021	1,986,435	2,009,000
Change in plan assets:
Fair value of plan assets, beginning of period	1,899,889	1,841,967
Actual return on plan assets	320,144	188,376
Company contributions	25,000	25,000
Plan participant contributions	0	0
Benefits paid	82,148	155,454
Fair value of plan assets, end of period	2,162,885	1,899,889	1,841,967
Funded status of the plans, December 31	(38,136)	(86,546)
Prepaid benefit costs (long-term assets)	19,816	0
Accrued benefit liability (current liabilities)	(3,346)	(2,104)
Accrued benefit liability (long-term liabilities)	(54,606)	(84,442)
Net amount recognized	(38,136)	(86,546)
Postretirement Health Coverage
Change in benefit obligation:
Benefit obligation, beginning of period	346,431	354,739
Service cost	7,500	7,478	8,259
Interest cost	13,648	14,814	14,166
Actuarial losses (gains)	(8,408)	(4,647)
Plan participant contributions	2,525	2,669
Plan amendments	0	0
Benefits paid	(23,208)	(28,622)
Benefit obligation, end of period	338,488	346,431	354,739
Change in plan assets:
Fair value of plan assets, beginning of period	170,092	156,765
Actual return on plan assets	32,445	13,327
Company contributions	15,000	0
Plan participant contributions	2,525	2,669
Benefits paid	2,525	2,669
Fair value of plan assets, end of period	217,537	170,092	$ 156,765
Funded status of the plans, December 31	(120,951)	(176,339)
Prepaid benefit costs (long-term assets)	0	0
Accrued benefit liability (current liabilities)	(2,198)	(3,072)
Accrued benefit liability (long-term liabilities)	(118,753)	(173,267)
Net amount recognized	$ (120,951)	$ (176,339)