Segment Information - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 688.9	$ 732.6
Segment income	67.6	92.7
Aquatic Systems
Segment Reporting Information [Line Items]
Net sales	220.5	240.4
Segment income	52.4	60.0
Filtration Solutions
Segment Reporting Information [Line Items]
Net sales	239.3	251.6
Segment income	33.7	33.7
Flow Technologies
Segment Reporting Information [Line Items]
Net sales	228.7	240.3
Segment income	30.1	38.7
Other
Segment Reporting Information [Line Items]
Net sales	0.4	0.3
Segment income	(17.5)	(15.4)
Operating Segments
Segment Reporting Information [Line Items]
Segment income	$ 98.7	$ 117.0