Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
NET EARNINGS	$ 69,285	$ 18,495	$ 23,488
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(131)	129	(82)
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	(40,934)	3,179	18,818
TOTAL COMPREHENSIVE INCOME (LOSS), net of tax	40,943	35,341	42,634
Pension Plans [Member]
Other comprehensive income (loss), net of tax	(28,467)	16,513	20,214
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	(41,051)	3,116	18,424
Income tax (expense) or benefit	9,037	(7,304)	(11,682)
Post-Retirement Plans [Member]
Other comprehensive income (loss), net of tax	256	204	(986)
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	117	63	394
Income tax (expense) or benefit	$ (80)	$ (91)	$ 560