Restructuring - Additional Information (Detail) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Person	Jun. 30, 2017 USD ($)	Dec. 31, 2017 Person
Restructuring Cost and Reserve [Line Items]
Number of employees | Person			250		250
Total restructuring costs	$ 25.0	$ 5.9	$ 30.6	$ 17.5
Aquatic Systems
Restructuring Cost and Reserve [Line Items]
Number of employees | Person			25		50
Total restructuring costs	1.2	0.0	$ 3.0	1.6
Filtration Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees | Person			100		125
Total restructuring costs	11.5	5.3	$ 13.5	6.7
Flow Technologies
Restructuring Cost and Reserve [Line Items]
Number of employees | Person			125		75
Total restructuring costs	6.3	0.5	$ 8.0	1.9
Other
Restructuring Cost and Reserve [Line Items]
Total restructuring costs	$ 6.0	$ 0.1	$ 6.1	$ 7.3