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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 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	$ 236	$ 612	3,155	$ (1,475)
Balance at the end of the period	1,522,080		1,522,080
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(38,009)	(38,706)	(38,670)	(39,441)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI	331	365	992	1,100
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	331	365	992	1,100
Balance at the end of the period	(37,678)	(38,341)	(37,678)	(38,341)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(5,416)	(5,399)	(6,315)	(3,591)
Other comprehensive income (loss) before reclassifications	(351)	376	548	(1,432)
Amounts reclassified from AOCI	0	0	0	0
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	(351)	376	548	(1,432)
Balance at the end of the period	(5,767)	(5,023)	(5,767)	(5,023)
Unrealized Gain (Loss) in Fair Value of Investments, Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	895	(700)	(464)	314
Other comprehensive income (loss) before reclassifications	254	(145)	1,633	(1,159)
Amounts reclassified from AOCI	2	16	(18)	16
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	256	(129)	1,615	(1,143)
Balance at the end of the period	1,151	(829)	1,151	(829)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period	(42,530)	(44,805)	(45,449)	(42,718)
Other comprehensive income (loss) before reclassifications	(97)	231	2,181	(2,591)
Amounts reclassified from AOCI	333	381	974	1,116
TOTAL OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX	236	612	3,155	(1,475)
Balance at the end of the period	$ (42,294)	$ (44,193)	$ (42,294)	$ (44,193)