Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Operating Lease Obligations [Line Items]
Rental expense under operating leases with initial terms exceeding	$ 222,000	$ 192,000	$ 444,000	$ 372,000
Letter of Credit
Operating Lease Obligations [Line Items]
Unused letters of credit, total	$ 1,580,000		$ 1,580,000