Income Taxes - Schedule of Reconciliation Difference of Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Income Tax Disclosure [Abstract]
Amount at statutory U.S. federal income tax rate	$ 6,465	$ 7,126		$ 5,707
Change because of the following items:
State income taxes, net of federal benefit	118	278		236
Stock-based compensation	21	25		36
Valuation allowance change	120	(699)		303
Tax reserve release	(121)	(128)		(77)
Federal manufacturing deduction	(235)	(266)		(220)
Federal research and development credit	(67)	(324)	(200)
Other	(36)	(231)		192
Income tax provision	$ 6,265	$ 5,781		$ 6,177