Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
NET EARNINGS (LOSS)	$ 24,634	$ (53,726)	$ 40,512	$ (43,738)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(123)	99	(139)	136
OTHER COMPREHENSIVE INCOME (LOSS):
TOTAL COMPREHENSIVE INCOME (LOSS), net of tax	25,240	(52,355)	41,831	(41,059)
Pension Plans [Member]
Other comprehensive income (loss), net of tax	687	1,235	1,374	2,469
OTHER COMPREHENSIVE INCOME (LOSS):
Income tax (expense) or benefit	(200)	(702)	(400)	(1,405)
Post-Retirement Plans [Member]
Other comprehensive income (loss), net of tax	42	37	84	74
OTHER COMPREHENSIVE INCOME (LOSS):
Income tax (expense) or benefit	(13)	$ (21)	(26)	(42)
Retained Earnings [Member]
OTHER COMPREHENSIVE INCOME (LOSS):
TOTAL COMPREHENSIVE INCOME (LOSS), net of tax	$ 24,634		$ 40,512	$ (43,738)