SEGMENT REPORTING - Identifiable Assets by Segments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total Identifiable Assets	$ 730,071	$ 645,226
Corporate
Segment Reporting Information [Line Items]
Total Identifiable Assets	45,100	54,700
Service Centers
Segment Reporting Information [Line Items]
Total Identifiable Assets	460,604	402,944
Innovative Pumping Solutions
Segment Reporting Information [Line Items]
Total Identifiable Assets	209,742	188,765
Supply Chain Services
Segment Reporting Information [Line Items]
Total Identifiable Assets	$ 59,725	$ 53,517