Segment Information - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Net sales	$ 780.6	$ 754.0	$ 1,513.2	$ 1,437.3
Segment income	122.6	129.2	215.3	191.1
Aquatic Systems
Segment Reporting Information [Line Items]
Net sales	276.2	253.7	516.6	476.2
Segment income	79.6	74.3	139.6	129.8
Filtration Solutions
Segment Reporting Information [Line Items]
Net sales	262.1	263.8	513.7	494.6
Segment income	52.3	49.0	86.0	73.0
Flow Technologies
Segment Reporting Information [Line Items]
Net sales	241.9	236.2	482.2	465.8
Segment income	44.4	40.3	83.1	73.4
Other
Segment Reporting Information [Line Items]
Net sales	0.4	0.3	0.7	0.7
Segment income	(12.2)	(12.0)	(27.6)	(27.6)
Operating Segments
Segment Reporting Information [Line Items]
Segment income	$ 164.1	$ 151.6	$ 281.1	$ 248.6