Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
NET EARNINGS	$ 32,115	$ 61,202	$ 69,285
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(2)	1,467	(131)
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	(25,638)	20,800	(40,934)
TOTAL COMPREHENSIVE INCOME, net of tax	15,325	90,698	40,943
Pension Plans [Member]
Other comprehensive income (loss), net of tax	(16,941)	27,890	(28,467)
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	(25,712)	20,793	(41,051)
Income tax (expense) or benefit	5,008	(8,431)	9,037
Post-Retirement Plans [Member]
Other comprehensive income (loss), net of tax	153	139	256
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	74	7	117
Income tax (expense) or benefit	$ (45)	$ (40)	$ (80)