Income Taxes - Schedule of Reconciliation Difference of Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Income Tax Disclosure [Abstract]
Amount at statutory U.S. federal income tax rate	$ 6,385	$ 6,465	$ 7,126
Change because of the following items:
State income taxes, net of federal benefit	67	118	278
Stock-based compensation	16	21	25
Valuation allowance change	348	120	(699)
Tax reserve change	34	(121)	(128)
Federal manufacturing deduction	(268)	(235)	(266)
Federal research and development credit	(74)	(67)	(324)
Other	(214)	(36)	(231)
Income tax provision	$ 6,294	$ 6,265	$ 5,781