COMPREHENSIVE EARNINGS (LOSS) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	$ 711,364
Balance at the end of the period	733,840	$ 711,364
Foreign Currency Derivatives
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(76)	(1,675)
Other comprehensive earnings (loss) before reclassifications	152	325
Reclassifications from accumulated other comprehensive loss	(25)	1,274
Other comprehensive earnings (loss) net of tax	127	1,599
Balance at the end of the period	51	(76)
Investments
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(697)	(605)
Other comprehensive earnings (loss) before reclassifications	(192)	(95)
Reclassifications from accumulated other comprehensive loss		3
Other comprehensive earnings (loss) net of tax	(192)	(92)
Balance at the end of the period	(889)	(697)
Postretirement and Pension Benefits
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	4,873	6,387
Other comprehensive earnings (loss) before reclassifications	(651)	(466)
Reclassifications from accumulated other comprehensive loss	(933)	(1,048)
Other comprehensive earnings (loss) net of tax	(1,584)	(1,514)
Balance at the end of the period	3,289	4,873
Foreign Currency Translation Adjustment
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(25,460)	(21,644)
Other comprehensive earnings (loss) before reclassifications	1,198	(3,816)
Other comprehensive earnings (loss) net of tax	1,198	(3,816)
Balance at the end of the period	(24,262)	(25,460)
Commodity Derivatives
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	1,114	173
Other comprehensive earnings (loss) before reclassifications	(1,050)	1,481
Reclassifications from accumulated other comprehensive loss	(44)	(540)
Other comprehensive earnings (loss) net of tax	(1,094)	941
Balance at the end of the period	20	1,114
Accumulated Other Comprehensive Earnings ( Loss )
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(20,246)	(17,364)
Other comprehensive earnings (loss) before reclassifications	(543)	(2,571)
Reclassifications from accumulated other comprehensive loss	(1,002)	(311)
Other comprehensive earnings (loss) net of tax	(1,545)	(2,882)
Balance at the end of the period	$ (21,791)	$ (20,246)