Segment information - Operations by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Customer revenue	$ 1,699.9	$ 1,745.8	$ 1,716.8
Gross profit	529.6	572.0	483.0
Total assets	2,065.6	2,419.5	2,707.9
DWS
Segment Reporting Information [Line Items]
Customer revenue	509.9	574.5	594.9
CA&I
Segment Reporting Information [Line Items]
Customer revenue	520.3	485.6	454.4
ECS
Segment Reporting Information [Line Items]
Customer revenue	669.7	685.7	667.5
Intersegment Eliminations
Segment Reporting Information [Line Items]
Customer revenue	0.0	1.4	0.1
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	1.4	0.1
Operating Segments
Segment Reporting Information [Line Items]
Customer revenue	1,699.9	1,747.2	1,716.9
Gross profit	550.8	562.3	458.6
Depreciation and amortization	159.2	129.1	119.3
Total assets	1,190.6	1,237.2	1,003.5
Capital expenditures	68.4	78.9	83.4
Operating Segments | DWS
Segment Reporting Information [Line Items]
Customer revenue	509.9	574.5	594.9
Gross profit	71.5	79.3	57.8
Depreciation and amortization	38.9	18.6	14.6
Total assets	346.5	353.5	216.9
Capital expenditures	6.3	13.5	13.6
Operating Segments | CA&I
Segment Reporting Information [Line Items]
Customer revenue	520.3	485.6	454.4
Gross profit	47.3	47.2	16.5
Depreciation and amortization	42.3	55.0	49.1
Total assets	268.3	289.6	229.6
Capital expenditures	6.5	13.2	24.5
Operating Segments | ECS
Segment Reporting Information [Line Items]
Customer revenue	669.7	687.1	667.6
Gross profit	432.0	435.8	384.3
Depreciation and amortization	78.0	55.5	55.6
Total assets	575.8	594.1	557.0
Capital expenditures	$ 55.6	$ 52.2	$ 45.3