Goodwill and Intangible Assets - Components of Identifiable Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Cost	$ 240,799	$ 210,589
Accumulated Amortization	138,617	127,069
Net Book Value	102,182	83,520
Patents
Finite-Lived Intangible Assets [Line Items]
Cost	9,028	9,028
Accumulated Amortization	7,883	7,729
Net Book Value	1,145	1,299
Completed Technology
Finite-Lived Intangible Assets [Line Items]
Cost	67,510	61,662
Accumulated Amortization	56,686	54,777
Net Book Value	10,824	6,885
Trademarks and Trade Names
Finite-Lived Intangible Assets [Line Items]
Cost	9,417	9,244
Accumulated Amortization	5,522	4,969
Net Book Value	3,895	4,275
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Cost	154,844	130,655
Accumulated Amortization	68,526	59,594
Net Book Value	$ 86,318	$ 71,061