Goodwill and Acquired Intangible Assets (Narrative) (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2019 USD ($) Segment	Sep. 30, 2017 Segment	Sep. 30, 2018 USD ($)
Number of operating segments | Segment	2	3
Number of reportable segments | Segment	2
Intangible Assets, Net (Including Goodwill)	$ 1,408,128		$ 1,382,659
Estimated aggregate future amortization expense for intangible assets, 2020	49,000
Estimated aggregate future amortization expense for intangible assets, 2021	43,800
Estimated aggregate future amortization expense for intangible assets, 2022	30,800
Estimated aggregate future amortization expense for intangible assets, 2023	19,000
Estimated aggregate future amortization expense for intangible assets, 2024	8,400
Estimated aggregate future amortization expense for intangible assets, thereafter	18,900
Professional Services [Member]
Intangible Assets, Net (Including Goodwill)	45,700		30,200
Software Products [Member]
Intangible Assets, Net (Including Goodwill)	$ 1,362,400		$ 1,352,400