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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period			$ 1,553,023
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	$ 915	$ (76)	1,108	$ 1,074
Balance at the end of the period	1,598,577		1,598,577
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(40,597)	(37,995)	(40,865)	(38,242)
Amounts reclassified from AOCI	269	324	537	571
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	269	324	537	571
Balance at the end of the period	(40,328)	(37,671)	(40,328)	(37,671)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(4,918)	(3,673)	(4,864)	(4,603)
Other comprehensive gain (loss) before reclassifications	649	(258)	595	672
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	649	(258)	595	672
Balance at the end of the period	(4,269)	(3,931)	(4,269)	(3,931)
Unrealized Gain (Loss) in Fair Value of Investments, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	295	664	316	656
Other comprehensive gain (loss) before reclassifications	(3)	(153)	(24)	(145)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	(3)	(153)	(24)	(145)
Balance at the end of the period	292	511	292	511
Unrealized Gain (Loss) in Fair Value of Interest Rate Swap, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period		(11)		24
Other comprehensive gain (loss) before reclassifications		11		(24)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX		11		(24)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(45,220)	(41,015)	(45,413)	(42,165)
Other comprehensive gain (loss) before reclassifications	646	(400)	571	503
Amounts reclassified from AOCI	269	324	537	571
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	915	(76)	1,108	1,074
Balance at the end of the period	$ (44,305)	$ (41,091)	$ (44,305)	$ (41,091)