Other Comprehensive Income (Loss) (Schedule Of Changes In AOCI Balances By Component (After-Tax)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period			$ 1,713,275
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	$ 612	$ 1,007	(1,475)	$ 2,115
Balance at the end of the period	1,756,748		1,756,748
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(38,706)	(40,328)	(39,441)	(40,865)
Amounts reclassified from AOCI	365	269	1,100	806
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	365	269	1,100	806
Balance at the end of the period	(38,341)	(40,059)	(38,341)	(40,059)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(5,399)	(4,269)	(3,591)	(4,864)
Other comprehensive loss before reclassifications	376	726	(1,432)	1,321
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	376	726	(1,432)	1,321
Balance at the end of the period	(5,023)	(3,543)	(5,023)	(3,543)
Unrealized Gain (Loss) in Fair Value of Investments, Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(700)	292	314	316
Other comprehensive loss before reclassifications	(145)	12	(1,159)	(12)
Amounts reclassified from AOCI	16		16
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	(129)	12	(1,143)	(12)
Balance at the end of the period	(829)	304	(829)	304
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(44,805)	(44,305)	(42,718)	(45,413)
Other comprehensive loss before reclassifications	231	738	(2,591)	1,309
Amounts reclassified from AOCI	381	269	1,116	806
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	612	1,007	(1,475)	2,115
Balance at the end of the period	$ (44,193)	$ (43,298)	$ (44,193)	$ (43,298)