Revenue - Schedule of Reportable Segment Revenues, Disaggregated by Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation Of Revenue [Line Items]
Net service revenues	$ 673.6	$ 608.1	$ 1,879.9	$ 1,737.9
Operating Segments | Landscape Maintenance
Disaggregation Of Revenue [Line Items]
Net service revenues	521.2	451.2	1,193.2	1,125.6
Operating Segments | Snow Removal
Disaggregation Of Revenue [Line Items]
Net service revenues	3.4	5.1	285.2	163.1
Operating Segments | Maintenance Services
Disaggregation Of Revenue [Line Items]
Net service revenues	524.6	456.3	1,478.4	1,288.7
Operating Segments | Development Services
Disaggregation Of Revenue [Line Items]
Net service revenues	150.3	152.8	404.7	451.9
Eliminations
Disaggregation Of Revenue [Line Items]
Net service revenues	$ (1.3)	$ (1.0)	$ (3.2)	$ (2.7)