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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period			$ 1,809,177
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	$ 1,670	$ (1,209)	2,919	$ (2,087)
Balance at the end of the period	1,499,040		1,499,040
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(38,340)	(39,060)	(38,670)	(39,441)
Other comprehensive loss before reclassifications	0	0	0	0
Amounts reclassified from AOCI	331	354	661	735
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	331	354	661	735
Balance at the end of the period	(38,009)	(38,706)	(38,009)	(38,706)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(6,069)	(4,765)	(6,315)	(3,591)
Other comprehensive loss before reclassifications	653	(634)	899	(1,808)
Amounts reclassified from AOCI	0	0	0	0
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	653	(634)	899	(1,808)
Balance at the end of the period	(5,416)	(5,399)	(5,416)	(5,399)
Unrealized Gain (Loss) in Fair Value of Investments, Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	209	229	(464)	314
Other comprehensive loss before reclassifications	714	(929)	1,379	(1,014)
Amounts reclassified from AOCI	(28)	0	(20)	0
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	686	(929)	1,359	(1,014)
Balance at the end of the period	895	(700)	895	(700)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(44,200)	(43,596)	(45,449)	(42,718)
Other comprehensive loss before reclassifications	1,367	(1,563)	2,278	(2,822)
Amounts reclassified from AOCI	303	354	641	735
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	1,670	(1,209)	2,919	(2,087)
Balance at the end of the period	$ (42,530)	$ (44,805)	$ (42,530)	$ (44,805)