SEGMENT REPORTING - Identifiable Assets by Segments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total Identifiable Assets	$ 745,230	$ 645,226
Corporate
Segment Reporting Information [Line Items]
Total Identifiable Assets	41,400	54,700
Service Centers
Segment Reporting Information [Line Items]
Total Identifiable Assets	456,310	402,944
Innovative Pumping Solutions
Segment Reporting Information [Line Items]
Total Identifiable Assets	227,085	188,765
Supply Chain Services
Segment Reporting Information [Line Items]
Total Identifiable Assets	$ 61,835	$ 53,517