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Pension Plans And Other Postretirement Benefit Plans (Components Of Net Periodic Benefit Cost) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax $ (8,090) $ (7,568)  
Pension Plan And SERP [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax 7,665 7,321  
Service cost 20,406 18,302 $ 19,791
Interest cost 27,898 27,544 26,117
Expected return on plan assets (31,626) (27,547) (28,299)
Amortization of prior service cost 2 2 2
Net loss recognition 9,793 8,511 9,451
Net periodic benefit cost 26,473 26,812 27,062
Other Postretirement Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax 425 247  
Service cost 3,220 3,205 2,925
Interest cost 5,490 6,110 5,158
Expected return on plan assets (1,899) (1,861) (1,991)
Amortization of prior service cost (1,144) (1,208) (1,199)
Net loss recognition 4,934 5,728 5,095
Net periodic benefit cost $ 10,601 $ 11,974 $ 9,988