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Segment Information - Summary of Continuing Operations by Segment (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 314.4	$ 308.8	$ 324.3	$ 273.8	$ 279.4	$ 269.4	$ 291.0	$ 249.7	$ 1,221.3	$ 1,089.5	$ 898.5
Operating income									147.1	121.5	73.6
Interest expense									7.9	9.3	7.3
Pension settlement charges									0.0	0.0	6.1
Other expense (income), net									0.6	0.6	(0.8)
Income before income taxes									138.6	111.6	61.0
Total depreciation and amortization									41.5	36.4	30.0
Total assets	1,165.5				1,023.8				1,165.5	1,023.8	992.3
Total capital expenditures									35.4	14.1	8.0
Environmental Solutions
Segment Reporting Information [Line Items]
Net sales									992.9	863.5	692.6
Operating income									139.4	113.0	72.4
Total depreciation and amortization									38.1	32.6	25.7
Total assets	908.1				775.2				908.1	775.2	746.4
Total capital expenditures									31.6	11.1	5.2
Safety And Security Systems
Segment Reporting Information [Line Items]
Net sales									228.4	226.0	205.9
Operating income									38.6	34.1	27.0
Total depreciation and amortization									3.3	3.7	4.1
Total assets	222.6				211.5				222.6	211.5	211.8
Total capital expenditures									2.7	2.0	2.2
Corporate
Segment Reporting Information [Line Items]
Operating income									(30.9)	(25.6)	(25.8)
Total depreciation and amortization									0.1	0.1	0.2
Total assets	34.5				36.7				34.5	36.7	33.6
Total capital expenditures									1.1	1.0	0.6
Segment, Continuing Operations
Segment Reporting Information [Line Items]
Total assets	1,165.2				1,023.4				1,165.2	1,023.4	991.8
Segment, Discontinued Operations
Segment Reporting Information [Line Items]
Total assets	$ 0.3				$ 0.4				$ 0.3	$ 0.4	$ 0.5