Acquisitions (Details) - USD ($) $ in Thousands					1 Months Ended	12 Months Ended
	Nov. 01, 2017	May 01, 2017	Oct. 20, 2016	Aug. 17, 2015	Jan. 31, 2017	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2016
Business Acquisition
Purchase price allocation, goodwill						$ 67,424		$ 49,314
Payments anticipated to be made						5,400
Machinery and equipment		$ 200
Liabilities assumed		600
Carolina Meter
Business Acquisition
Total purchase consideration	$ 6,200
Cash payment	2,000
Pre-existing receivables	$ 4,200
Receivables						600
Inventory						300
Purchase price allocation, intangibles						3,300
Purchase price allocation, goodwill						2,000
D-Flow Technology AB
Business Acquisition
Cash payment		23,200
Receivables		300
Inventory		600
Purchase price allocation, intangibles		10,900
Purchase price allocation, goodwill		$ 11,800
Percent of voting interest acquired		100.00%
Nice Instruments
Business Acquisition
Total purchase consideration			$ 2,000
Cash payment					$ 200
Purchase price allocation, intangibles						700
Purchase price allocation, goodwill						1,300
Purchase price allocation, inventory and equipment						$ 15
Customer technology | Nice Instruments
Business Acquisition
Estimated average useful life						15 years
National Meter and Automation, Inc. | United Utilities, Inc.
Business Acquisition
Total purchase consideration				$ 3,300
Cash payment				400
Pre-existing receivables				$ 2,900
Receivables							$ 800
Inventory							400
Purchase price allocation, goodwill							300
Property, plant and equipment							100
Intangibles							$ 1,700
National Meter and Automation, Inc. | Customer relationships | United Utilities, Inc.
Business Acquisition
Estimated average useful life							12 years