SEGMENT REPORTING - Identifiable Assets by Segments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total Identifiable Assets	$ 744,678	$ 645,226
Corporate
Segment Reporting Information [Line Items]
Total Identifiable Assets	46,900	54,700
Service Centers
Segment Reporting Information [Line Items]
Total Identifiable Assets	458,975	402,944
Innovative Pumping Solutions
Segment Reporting Information [Line Items]
Total Identifiable Assets	225,361	188,765
Supply Chain Services
Segment Reporting Information [Line Items]
Total Identifiable Assets	$ 60,342	$ 53,517