Other Comprehensive Income (Loss) (Schedule Of Changes In AOCI Balances By Component (After-Tax)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	$ 1,809,177
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	1,249	$ (878)
Balance at the end of the period	1,812,489
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(38,670)	(39,441)
Amounts reclassified from AOCI	330	381
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	330	381
Balance at the end of the period	(38,340)	(39,060)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(6,315)	(3,591)
Other comprehensive loss before reclassifications	246	(1,174)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	246	(1,174)
Balance at the end of the period	(6,069)	(4,765)
Unrealized Gain (Loss) in Fair Value of Investments, Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(464)	314
Other comprehensive loss before reclassifications	665	(85)
Amounts reclassified from AOCI	8
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	673	(85)
Balance at the end of the period	209	229
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(45,449)	(42,718)
Other comprehensive loss before reclassifications	911	(1,259)
Amounts reclassified from AOCI	338	381
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	1,249	(878)
Balance at the end of the period	$ (44,200)	$ (43,596)