Income Taxes - Summary of Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Beginning of fiscal year	$ 1,508	$ 1,248	$ 1,216
Increases in tax positions for prior years	8	77	50
Decreases in tax positions for prior years	(35)	(21)	(10)
Increases in tax positions for current year	216	365	146
Lapse of the statute of limitations	(216)	(161)	(154)
End of fiscal year	$ 1,481	$ 1,508	$ 1,248