Goodwill and Intangible Assets - Components of Identifiable Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Cost	$ 385,518	$ 198,918
Accumulated Amortization	106,285	98,962
Net Book Value	279,233	99,956
Patents
Finite-Lived Intangible Assets [Line Items]
Cost	5,302	5,302
Accumulated Amortization	4,401	4,325
Net Book Value	901	977
Completed Technology
Finite-Lived Intangible Assets [Line Items]
Cost	88,475	44,829
Accumulated Amortization	30,790	28,934
Net Book Value	57,685	15,895
Trademarks and Trade Names
Finite-Lived Intangible Assets [Line Items]
Cost	25,316	6,298
Accumulated Amortization	3,444	2,953
Net Book Value	21,872	3,345
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Cost	266,425	142,489
Accumulated Amortization	67,650	62,750
Net Book Value	$ 198,775	$ 79,739