Other Comprehensive Income (Loss) (Schedule Of Changes In AOCI Balances By Component (After-Tax)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	$ 1,440,142
Total other comprehensive income (loss), Net of Tax	(1,028)	$ 1,249
Balance	1,459,298
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(42,100)	(45,449)
Other comprehensive income (loss) before reclassifications	(1,447)	911
Amounts reclassified from AOCI	419	338
Total other comprehensive income (loss), Net of Tax	(1,028)	1,249
Balance	(43,128)	(44,200)
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(37,826)	(38,670)
Other comprehensive income (loss) before reclassifications	0
Amounts reclassified from AOCI	423	330
Total other comprehensive income (loss), Net of Tax	423	330
Balance	(37,403)	(38,340)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(5,371)	(6,315)
Other comprehensive income (loss) before reclassifications	(1,993)	246
Amounts reclassified from AOCI	0
Total other comprehensive income (loss), Net of Tax	(1,993)	246
Balance	(7,364)	(6,069)
Unrealized Gain (Loss) In Fair Value Of Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	1,097	(464)
Other comprehensive income (loss) before reclassifications	546	665
Amounts reclassified from AOCI	(4)	8
Total other comprehensive income (loss), Net of Tax	542	673
Balance	$ 1,639	$ 209