Goodwill and Intangible Assets - Intangible Assets Subject to Amortization (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 110,987	$ 114,505
Accumulated Amortization	(96,451)	(93,320)
Total	$ 14,536	$ 21,185
Average Life	6 years	6 years
Completed technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 82,295	$ 84,955
Accumulated Amortization	(77,400)	(77,682)
Total	$ 4,895	$ 7,273
Average Life	5 years	5 years
Customer contracts and relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 28,692	$ 28,947
Accumulated Amortization	(19,051)	(15,091)
Total	$ 9,641	$ 13,856
Average Life	8 years	8 years
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 0	$ 603
Accumulated Amortization	0	(547)
Total	$ 0	$ 56
Average Life	0 years	3 years