Other Comprehensive Income (Loss) (Schedule Of Changes In AOCI Balances By Component (After-Tax)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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	(878)	$ 193
Balance at the end of the period	1,699,680
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(39,441)	(40,865)
Amounts reclassified from AOCI	381	268
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	381	268
Balance at the end of the period	(39,060)	(40,597)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(3,591)	(4,864)
Other comprehensive loss before reclassifications	(1,174)	(54)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	(1,174)	(54)
Balance at the end of the period	(4,765)	(4,918)
Unrealized Gain in Fair Value of Investments, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	314	316
Other comprehensive loss before reclassifications	(85)	(21)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	(85)	(21)
Balance at the end of the period	229	295
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(42,718)	(45,413)
Other comprehensive loss before reclassifications	(1,259)	(75)
Amounts reclassified from AOCI	381	268
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	(878)	193
Balance at the end of the period	$ (43,596)	$ (45,220)