Segment information - Operations by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Customer revenue	$ 1,725.1	$ 1,699.9	$ 1,745.8
Gross profit	551.3	529.6	572.0
Total assets	1,965.4	2,065.6	2,419.5
DWS
Segment Reporting Information [Line Items]
Customer revenue	546.1	509.9	574.5
CA&I
Segment Reporting Information [Line Items]
Customer revenue	531.0	520.3	485.6
ECS
Segment Reporting Information [Line Items]
Customer revenue	648.0	669.7	685.7
Intersegment Eliminations
Segment Reporting Information [Line Items]
Customer revenue	0.0	0.0	(1.4)
Intersegment Eliminations | DWS
Segment Reporting Information [Line Items]
Customer revenue	0.0	0.0	0.0
Intersegment Eliminations | CA&I
Segment Reporting Information [Line Items]
Customer revenue	0.0	0.0	0.0
Intersegment Eliminations | ECS
Segment Reporting Information [Line Items]
Customer revenue	0.0	0.0	(1.4)
Operating Segments
Segment Reporting Information [Line Items]
Customer revenue	1,725.1	1,699.9	1,747.2
Gross profit	554.7	550.8	562.3
Depreciation and amortization	121.8	159.2	129.1
Total assets	1,196.6	1,190.6	1,237.2
Capital expenditures	65.9	68.4	78.9
Operating Segments | DWS
Segment Reporting Information [Line Items]
Customer revenue	546.1	509.9	574.5
Gross profit	76.2	71.5	79.3
Depreciation and amortization	29.2	38.9	18.6
Total assets	379.2	346.5	353.5
Capital expenditures	3.9	6.3	13.5
Operating Segments | CA&I
Segment Reporting Information [Line Items]
Customer revenue	531.0	520.3	485.6
Gross profit	81.9	47.3	47.2
Depreciation and amortization	29.8	42.3	55.0
Total assets	249.6	268.3	289.6
Capital expenditures	7.1	6.5	13.2
Operating Segments | ECS
Segment Reporting Information [Line Items]
Customer revenue	648.0	669.7	687.1
Gross profit	396.6	432.0	435.8
Depreciation and amortization	62.8	78.0	55.5
Total assets	567.8	575.8	594.1
Capital expenditures	$ 54.9	$ 55.6	$ 52.2