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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period			$ 1,440,142
Total other comprehensive income (loss), net of tax	$ 2,531	$ 1,670	1,503	$ 2,919
Balance at the end of the period	1,484,917		1,484,917
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(43,128)	(44,200)	(42,100)	(45,449)
Other comprehensive income (loss) before reclassifications	2,136	1,367	689	2,278
Amounts reclassified from AOCI	395	303	814	641
Total other comprehensive income (loss), net of tax	2,531	1,670	1,503	2,919
Balance at the end of the period	(40,597)	(42,530)	(40,597)	(42,530)
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(37,403)	(38,340)	(37,826)	(38,670)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI	424	331	847	661
Total other comprehensive income (loss), net of tax	424	331	847	661
Balance at the end of the period	(36,979)	(38,009)	(36,979)	(38,009)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(7,364)	(6,069)	(5,371)	(6,315)
Other comprehensive income (loss) before reclassifications	801	653	(1,192)	899
Amounts reclassified from AOCI	0	0	0	0
Total other comprehensive income (loss), net of tax	801	653	(1,192)	899
Balance at the end of the period	(6,563)	(5,416)	(6,563)	(5,416)
Unrealized Gain (Loss) In Fair Value Of Investments, Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	1,639	209	1,097	(464)
Other comprehensive income (loss) before reclassifications	1,335	714	1,881	1,379
Amounts reclassified from AOCI	(29)	(28)	(33)	(20)
Total other comprehensive income (loss), net of tax	1,306	686	1,848	1,359
Balance at the end of the period	$ 2,945	$ 895	$ 2,945	$ 895