Revenue - Schedule of Reportable Segment Revenues, Disaggregated by Revenue (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2019	Sep. 30, 2018
Disaggregation Of Revenue [Line Items]
Net service revenues	$ 1,713.6	$ 2,404.6	$ 2,353.6
Operating Segments | Landscape Maintenance
Disaggregation Of Revenue [Line Items]
Net service revenues	1,132.5	1,568.3	1,522.5
Operating Segments | Snow Removal
Disaggregation Of Revenue [Line Items]
Net service revenues	145.8	245.1	252.3
Operating Segments | Maintenance Services
Disaggregation Of Revenue [Line Items]
Net service revenues	1,278.3	1,813.4	1,774.8
Operating Segments | Development Services
Disaggregation Of Revenue [Line Items]
Net service revenues	437.7	595.4	583.3
Eliminations
Disaggregation Of Revenue [Line Items]
Net service revenues	$ (2.4)	$ (4.2)	$ (4.5)