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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period			$ 1,420,227
Other comprehensive income (loss)	$ (242)	$ (1,330)	832	$ (3,043)
Balance at the end of the period	1,524,044		1,524,044
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(37,671)	(40,268)	(38,242)	(40,268)
Amounts reclassified from AOCI	248		819
Other comprehensive income (loss)	248		819
Balance at the end of the period	(37,423)	(40,268)	(37,423)	(40,268)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(3,931)	(3,123)	(4,603)	(1,389)
Other comprehensive income (loss) before reclassifications	(411)		261
Other comprehensive income (loss)	(411)	(1,375)	261	(3,109)
Balance at the end of the period	(4,342)	(4,498)	(4,342)	(4,498)
Unrealized Gain (Loss) in Fair Value of Investments, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	511	(194)	656	(110)
Other comprehensive income (loss) before reclassifications	(79)		(224)
Other comprehensive income (loss)	(79)	(2)	(224)	(86)
Balance at the end of the period	432	(196)	432	(196)
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		254	24	149
Other comprehensive income (loss) before reclassifications			(24)
Other comprehensive income (loss)		47	(24)	152
Balance at the end of the period		301		301
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(41,091)	(43,331)	(42,165)	(41,618)
Other comprehensive income (loss) before reclassifications	(490)		13
Amounts reclassified from AOCI	248		819
Other comprehensive income (loss)	(242)	(1,330)	832	(3,043)
Balance at the end of the period	$ (41,333)	$ (44,661)	$ (41,333)	$ (44,661)