SEGMENT INFORMATION (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment information
Number of operating segments | segment			1
Revenues derived from foreign subsidiaries			$ 82,485,000	$ 74,698
Identifiable assets	$ 310,550,000		$ 310,550,000		$ 285,301,000
Total Revenue
Segment information
Percentage of concentration risk	15.00%	20.00%	16.00%	20.00%
Trade receivables
Segment information
Percentage of concentration risk			17.00%		13.00%
Outside the United States
Segment information
Revenues derived from foreign subsidiaries	$ 38,802,000	$ 38,395,000
Wholly owned foreign subsidiaries
Segment information
Revenues derived from foreign subsidiaries	29,985,000	$ 33,497,000	$ 64,567,000	$ 65,903,000
Identifiable assets	$ 93,952,000		$ 93,952,000		$ 88,400,000