Income Taxes - Summary of Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Beginning of fiscal year	$ 1,481	$ 1,508	$ 1,248
Increases in tax positions for prior years	61	8	77
Decreases in tax positions for prior years		(35)	(21)
Increases in tax positions for current year	735	216	365
Settlements with taxing authorities	(613)
Lapse of the statute of limitations	(105)	(216)	(161)
End of fiscal year	$ 1,559	$ 1,481	$ 1,508