Goodwill and Intangible Assets - Amortization Expense Associated with Intangible Assets (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets	[1]	$ 1,503	$ 1,684	$ 3,005	$ 3,472
Completed Technology
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets		494	615	988	1,321
Other Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets		$ 1,009	$ 1,069	$ 2,017	$ 2,151

[1] Cost of revenues and selling, general and administrative expenses exclude the amortization of intangible assets. See Note 4.