SEGMENT AND GEOGRAPHICAL REPORTING, Business Segmented Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Sales	$ 265,700	$ 251,900	$ 250,700	$ 238,500	$ 222,300	$ 230,000	$ 256,200	$ 253,600	$ 278,600	$ 303,100	$ 323,700	$ 341,600	$ 1,006,782	$ 962,092	$ 1,247,043
Operating income for reportable segments, excluding amortization													90,124	72,950	113,967
Identifiable assets at year end	618,224				590,255				660,710				618,224	590,255	660,710
Capital expenditures													2,646	4,403	12,172
Proceeds from sale of fixed assets													0	(1,206)	0
Depreciation													9,463	10,480	10,891
Amortization													17,266	18,061	20,621
Interest expense													17,054	15,564	10,932
Impairment of goodwill and other intangible assets													0	0	68,735
Reportable Segment [Member] | Service Centers [Member]
Segment Reporting Information [Line Items]
Sales													641,275	621,007	826,588
Operating income for reportable segments, excluding amortization													63,250	47,634	78,170
Identifiable assets at year end	385,744				370,261				451,333				385,744	370,261	451,333
Capital expenditures													1,076	447	3,185
Proceeds from sale of fixed assets														(1,038)
Depreciation													5,162	6,520	7,734
Amortization													8,989	9,152	10,334
Interest expense													9,712	9,290	2,967
Impairment of goodwill and other intangible assets															15,842
Reportable Segment [Member] | Innovative Pumping Solutions [Member]
Segment Reporting Information [Line Items]
Sales													204,030	187,124	254,829
Operating income for reportable segments, excluding amortization													11,423	9,867	21,584
Identifiable assets at year end	172,538				175,198				159,365				172,538	175,198	159,365
Capital expenditures													1,488	3,827	8,383
Proceeds from sale of fixed assets														(168)
Depreciation													4,198	3,834	2,930
Amortization													7,194	7,826	8,406
Interest expense													5,352	4,422	6,881
Impairment of goodwill and other intangible assets															52,893
Reportable Segment [Member] | Supply Chain Services [Member]
Segment Reporting Information [Line Items]
Sales													161,477	153,961	165,626
Operating income for reportable segments, excluding amortization													15,451	15,449	14,213
Identifiable assets at year end	$ 59,942				$ 44,796				$ 50,012				59,942	44,796	50,012
Capital expenditures													82	129	604
Proceeds from sale of fixed assets														0
Depreciation													103	126	227
Amortization													1,083	1,083	1,881
Interest expense													$ 1,990	$ 1,852	1,084
Impairment of goodwill and other intangible assets															$ 0