ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Components of accumulated other comprehensive loss [Roll Forward]
Balance			$ 616,881
Other comprehensive loss	$ (2,895)	$ 2,708	(1,519)	$ 3,259
Balance	663,220		663,220
AOCI Attributable to Parent [Member]
Components of accumulated other comprehensive loss [Roll Forward]
Balance			(1,642)
Balance	(3,161)		(3,161)
Foreign Currency Translation Adjustment [Member]
Components of accumulated other comprehensive loss [Roll Forward]
Balance			(1,303)
Other comprehensive loss			(1,548)
Balance	(2,851)		(2,851)
Postretirement Benefit Plan [Member]
Components of accumulated other comprehensive loss [Roll Forward]
Balance			(339)
Other comprehensive loss			29
Balance	$ (310)		$ (310)