SEGMENT REPORTING, Business Segmented Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Sales	$ 285,936	$ 238,527
Income (loss) from operations	11,149	8,236
Reportable Segment [Member]
Segment Reporting Information [Line Items]
Sales	285,936	238,527
Amortization	4,358	4,316
Income (loss) from operations	21,908	16,592
Operating income, excluding amortization	26,266	20,908
Reportable Segment [Member] \| Service Centers [Member]
Segment Reporting Information [Line Items]
Sales	175,362	148,713
Amortization	2,459	2,250
Income (loss) from operations	13,371	11,090
Operating income, excluding amortization	15,830	13,340
Reportable Segment [Member] \| Innovative Pumping Solutions [Member]
Segment Reporting Information [Line Items]
Sales	67,642	49,058
Amortization	1,627	1,795
Income (loss) from operations	4,755	1,715
Operating income, excluding amortization	6,382	3,510
Reportable Segment [Member] \| Supply Chain Services [Member]
Segment Reporting Information [Line Items]
Sales	42,932	40,756
Amortization	272	271
Income (loss) from operations	3,782	3,787
Operating income, excluding amortization	$ 4,054	$ 4,058

Operating income for reportable segments excluding amortization of intangibles.

No definition available.

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- Definition

The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

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- Definition

Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Details

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