SEGMENT INFORMATION (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment information
Number of operating segments | segment			1
Revenues derived from foreign subsidiaries			$ 122,020,000	$ 111,073
Identifiable assets	$ 308,242,000		$ 308,242,000		$ 285,301,000
Total Revenue
Segment information
Percentage of concentration risk	17.00%	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	$ 39,534,000	$ 36,216,000
Wholly owned foreign subsidiaries
Segment information
Revenues derived from foreign subsidiaries	31,894,000	$ 30,717,000	$ 96,461,000	$ 96,618,000
Identifiable assets	$ 92,403,000		$ 92,403,000		$ 88,400,000