Pension Plans And Other Post-Retirement Benefits (Schedule Of Fair Value Of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 266,461	$ 239,007	$ 270,353
Pension Benefits [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	21,360	14,082
Pension Benefits [Member] | Assets Measured At NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	245,101	224,925
Pension Benefits [Member] | Common stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	17,166	12,268
Pension Benefits [Member] | Common stocks [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	17,166	12,268
Pension Benefits [Member] | International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	51,408	48,040
Pension Benefits [Member] | International equities [Member] | Assets Measured At NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	51,408	48,040
Pension Benefits [Member] | Real estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	13,970	15,766
Pension Benefits [Member] | Real estate [Member] | Assets Measured At NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	13,970	15,766
Pension Benefits [Member] | Hedge / Diversifying Strategies [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	38,099	37,591
Pension Benefits [Member] | Hedge / Diversifying Strategies [Member] | Assets Measured At NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	38,099	37,591
Pension Benefits [Member] | Credit [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	27,847	25,772
Pension Benefits [Member] | Credit [Member] | Assets Measured At NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	27,847	25,772
Pension Benefits [Member] | Liability Hedging Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	113,777	97,756
Pension Benefits [Member] | Liability Hedging Assets [Member] | Assets Measured At NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	113,777	97,756
Pension Benefits [Member] | Cash And Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	4,194	1,814
Pension Benefits [Member] | Cash And Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	4,194	1,814
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	54,011	45,422	$ 47,750
Other Postretirement Benefits [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	22,495	19,669
Other Postretirement Benefits [Member] | Assets Measured At NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	31,516	25,753
Other Postretirement Benefits [Member] | International equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	28,576	22,293
Other Postretirement Benefits [Member] | International equities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	10,795	8,411
Other Postretirement Benefits [Member] | International equities [Member] | Assets Measured At NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	17,781	13,882
Other Postretirement Benefits [Member] | Real estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	6,200	5,032
Other Postretirement Benefits [Member] | Real estate [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	2,449	1,967
Other Postretirement Benefits [Member] | Real estate [Member] | Assets Measured At NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	3,751	3,065
Other Postretirement Benefits [Member] | Liability Hedging Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	15,669	13,881
Other Postretirement Benefits [Member] | Liability Hedging Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	5,685	5,075
Other Postretirement Benefits [Member] | Liability Hedging Assets [Member] | Assets Measured At NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	9,984	8,806
Other Postretirement Benefits [Member] | Cash And Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	3,566	4,216
Other Postretirement Benefits [Member] | Cash And Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 3,566	$ 4,216