Other Comprehensive Income (Loss) (Schedule Of Changes In AOCI Balances By Component (After-Tax)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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	$ (1,209)	$ 915	(2,087)	$ 1,108
Balance at the end of the period	1,730,084		1,730,084
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(39,060)	(40,597)	(39,441)	(40,865)
Amounts reclassified from AOCI	354	269	735	537
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	354	269	735	537
Balance at the end of the period	(38,706)	(40,328)	(38,706)	(40,328)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(4,765)	(4,918)	(3,591)	(4,864)
Other comprehensive loss before reclassifications	(634)	649	(1,808)	595
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	(634)	649	(1,808)	595
Balance at the end of the period	(5,399)	(4,269)	(5,399)	(4,269)
Unrealized Gain (Loss) in Fair Value of Investments, Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	229	295	314	316
Other comprehensive loss before reclassifications	(929)	(3)	(1,014)	(24)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	(929)	(3)	(1,014)	(24)
Balance at the end of the period	(700)	292	(700)	292
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(43,596)	(45,220)	(42,718)	(45,413)
Other comprehensive loss before reclassifications	(1,563)	646	(2,822)	571
Amounts reclassified from AOCI	354	269	735	537
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	(1,209)	915	(2,087)	1,108
Balance at the end of the period	$ (44,805)	$ (44,305)	$ (44,805)	$ (44,305)