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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 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	$ 1,007	$ (242)	2,115	$ 832
Balance at the end of the period	1,627,923		1,627,923
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(40,328)	(37,671)	(40,865)	(38,242)
Amounts reclassified from AOCI	269	248	806	819
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	269	248	806	819
Balance at the end of the period	(40,059)	(37,423)	(40,059)	(37,423)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(4,269)	(3,931)	(4,864)	(4,603)
Other comprehensive gain (loss) before reclassifications	726	(411)	1,321	261
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	726	(411)	1,321	261
Balance at the end of the period	(3,543)	(4,342)	(3,543)	(4,342)
Unrealized Gain (Loss) in Fair Value of Investments, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	292	511	316	656
Other comprehensive gain (loss) before reclassifications	12	(79)	(12)	(224)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	12	(79)	(12)	(224)
Balance at the end of the period	304	432	304	432
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				24
Other comprehensive gain (loss) before reclassifications				(24)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX				(24)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(44,305)	(41,091)	(45,413)	(42,165)
Other comprehensive gain (loss) before reclassifications	738	(490)	1,309	13
Amounts reclassified from AOCI	269	248	806	819
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	1,007	(242)	2,115	832
Balance at the end of the period	$ (43,298)	$ (41,333)	$ (43,298)	$ (41,333)