Goodwill and Intangible Assets - Components of Identifiable Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Cost	$ 238,262	$ 210,589
Accumulated Amortization	132,505	127,069
Net Book Value	105,757	83,520
Patents
Finite-Lived Intangible Assets [Line Items]
Cost	9,028	9,028
Accumulated Amortization	7,806	7,729
Net Book Value	1,222	1,299
Completed Technology
Finite-Lived Intangible Assets [Line Items]
Cost	67,032	61,662
Accumulated Amortization	55,668	54,777
Net Book Value	11,364	6,885
Trademarks and Trade Names
Finite-Lived Intangible Assets [Line Items]
Cost	9,405	9,244
Accumulated Amortization	5,241	4,969
Net Book Value	4,164	4,275
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Cost	152,797	130,655
Accumulated Amortization	63,790	59,594
Net Book Value	$ 89,007	$ 71,061