Revenue - Schedule of Reportable Segment Revenues, Disaggregated by Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Net service revenues	$ 651.9	$ 559.1	$ 1,206.3	$ 1,129.8
Operating Segments | Landscape Maintenance
Disaggregation Of Revenue [Line Items]
Net service revenues	309.7	311.0	672.0	674.3
Operating Segments | Snow Removal
Disaggregation Of Revenue [Line Items]
Net service revenues	226.0	102.5	281.8	158.1
Operating Segments | Maintenance Services
Disaggregation Of Revenue [Line Items]
Net service revenues	535.7	413.5	953.8	832.4
Operating Segments | Development Services
Disaggregation Of Revenue [Line Items]
Net service revenues	117.1	146.3	254.4	299.1
Eliminations
Disaggregation Of Revenue [Line Items]
Net service revenues	$ (0.9)	$ (0.7)	$ (1.9)	$ (1.7)