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Note 1 - Summary of Significant Accounting Policies (Details Textual) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Percentage of LIFO Inventory		72.00%	73.00%
Depreciation, Total		$ 12,600	$ 13,300	$ 13,500
Goodwill, Impairment Loss		0	0
Advertising Expense		3,000	3,000	3,100
Performance Shares [Member]
Share-based Payment Arrangement, Expense		$ 700	$ 1,300	$ 400
2015 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		3 years
Customer Concentration Risk [Member] | Revenue Benchmark [Member]
Number of Major Customers		0	0	0
Customer Relationships [Member]
Impairment of Intangible Assets, Finite-lived				$ 3,200
Other Segments [Member]
Goodwill, Impairment Loss				0
Bayou City Pump Inc [Member]
Goodwill, Impairment Loss	$ 900			$ 900

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