Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
NET EARNINGS	$ 61,202	$ 69,285	$ 18,495
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	1,467	(131)	129
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	20,800	(40,934)	3,179
TOTAL COMPREHENSIVE INCOME, net of tax	90,698	40,943	35,341
Pension Plans [Member]
Other comprehensive income (loss), net of tax	27,890	(28,467)	16,513
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	20,793	(41,051)	3,116
Income tax (expense) or benefit	(8,431)	9,037	(7,304)
Post-Retirement Plans [Member]
Other comprehensive income (loss), net of tax	139	256	204
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	7	117	63
Income tax (expense) or benefit	$ (40)	$ (80)	$ (91)