Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
NET EARNINGS	$ 42,290	$ 137,505
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	0	0
OTHER COMPREHENSIVE INCOME (LOSS):
TOTAL COMPREHENSIVE INCOME, net of tax	43,688	138,255
Pension Plans [Member]
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	1,362	726
OTHER COMPREHENSIVE INCOME (LOSS):
Income tax (expense) or benefit	(402)	(215)
Post-Retirement Plans [Member]
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	36	24
OTHER COMPREHENSIVE INCOME (LOSS):
Income tax (expense) or benefit	$ (11)	$ (7)