Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
NET EARNINGS (LOSS)	$ 79,934	$ (104,926)	$ 122,224	$ 32,579
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	0	0	0	0
OTHER COMPREHENSIVE INCOME (LOSS):
TOTAL COMPREHENSIVE INCOME (LOSS), net of tax	81,332	(104,176)	125,020	34,079
Pension Plans [Member]
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	1,362	726	2,724	1,452
OTHER COMPREHENSIVE INCOME (LOSS):
Income tax (expense) or benefit	(402)	(215)	(804)	(430)
Post-Retirement Plans [Member]
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	36	24	72	48
OTHER COMPREHENSIVE INCOME (LOSS):
Income tax (expense) or benefit	$ (11)	$ (7)	$ (22)	$ (14)