Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
NET EARNINGS	$ 15,878	$ 9,988
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(16)	37
OTHER COMPREHENSIVE INCOME (LOSS):
TOTAL COMPREHENSIVE INCOME, net of tax	16,591	11,296
Pension Plans [Member]
Other comprehensive income (loss), net of tax	687	1,234
OTHER COMPREHENSIVE INCOME (LOSS):
Income tax (expense) or benefit	(200)	(703)
Post-Retirement Plans [Member]
Other comprehensive income (loss), net of tax	42	37
OTHER COMPREHENSIVE INCOME (LOSS):
Income tax (expense) or benefit	$ (13)	$ (21)