Note 3 - Revenue - Disaggregation of Revenue by Major Categories and Geographic Location (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net sales	$ 108,330	$ 111,827	$ 205,189	$ 208,431
UNITED STATES
Net sales	74,784	71,519	142,485	135,952
Non-US [Member]
Net sales	33,546	40,308	62,704	72,479
Pumps and Pump Systems [Member]
Net sales	92,167	97,784	174,688	178,611
Repair Parts for Pumps and Pump Systems and Other [Member]
Net sales	$ 16,163	$ 14,043	$ 30,501	$ 29,820

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration