Goodwill and Acquired Intangible Assets (Narrative) (Details) $ in Millions	12 Months Ended
	Sep. 30, 2018 USD ($) Segment	Sep. 30, 2017 USD ($) Segment
Number of operating segments | Segment	2	3
Number of reportable segments | Segment	2	3
Estimated aggregate future amortization expense for intangible assets, 2019	$ 50.6
Estimated aggregate future amortization expense for intangible assets, 2020	47.8
Estimated aggregate future amortization expense for intangible assets, 2021	42.3
Estimated aggregate future amortization expense for intangible assets, 2022	29.1
Estimated aggregate future amortization expense for intangible assets, 2023	17.1
Estimated aggregate future amortization expense for intangible assets, thereafter	13.2
Professional Services [Member]
Goodwill and acquired intangible assets	30.2	$ 30.6
Software Products [Member]
Goodwill and acquired intangible assets	$ 1,352.4	$ 1,410.0