Employee Benefit Plans and Other Postretirement Benefits (Schedule Of Obligation And Funded Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Postretirement Health Coverage
Change in benefit obligation:
Benefit obligation, beginning of period	$ 354,739	$ 361,006
Service cost	7,478	8,259	$ 7,015
Interest cost	14,814	14,166	16,878
Actuarial losses (gains)	(4,647)	(6,757)
Plan participant contributions	2,669	2,587
Plan amendments	0	0
Special early retirement benefits	0	622
Benefits paid, net of Medicare Part D subsidy	(28,622)	(25,144)
Benefit obligation, end of period	346,431	354,739	361,006
Change in plan assets:
Fair value of plan assets, beginning of period	156,765	156,840
Actual return on plan assets	13,327	(75)
Company contributions	0	0
Plan participant contributions	2,669	2,587
Benefits paid	(2,669)	(2,587)
Fair value of plan assets, end of period	170,092	156,765	156,840
Funded status of the plans, December 31	(176,339)	(197,974)
Accrued benefit liability (current liabilities)	(3,072)	(4,315)
Accrued benefit liability (long-term liabilities)	(173,267)	(193,659)
Net amount recognized	(176,339)	(197,974)
Pension and SERPA Benefits
Change in benefit obligation:
Benefit obligation, beginning of period	2,009,000	2,069,980
Service cost	33,437	40,039	31,498
Interest cost	90,827	87,345	86,923
Actuarial losses (gains)	13,481	(128,082)
Plan participant contributions	0	0
Plan amendments	0	6,407
Special early retirement benefits	0	10,563
Benefits paid, net of Medicare Part D subsidy	(160,310)	(77,252)
Benefit obligation, end of period	1,986,435	2,009,000	2,069,980
Change in plan assets:
Fair value of plan assets, beginning of period	1,841,967	1,992,646
Actual return on plan assets	188,376	(77,980)
Company contributions	25,000	0
Plan participant contributions	0	0
Benefits paid	(155,454)	(72,699)
Fair value of plan assets, end of period	1,899,889	1,841,967	$ 1,992,646
Funded status of the plans, December 31	(86,546)	(167,033)
Accrued benefit liability (current liabilities)	(2,104)	(2,145)
Accrued benefit liability (long-term liabilities)	(84,442)	(164,888)
Net amount recognized	$ (86,546)	$ (167,033)