Bank Credit Arrangements - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2016	Mar. 22, 2016	Sep. 30, 2015	Oct. 01, 2014
Debt Instrument [Line Items]
Credit facility with a commercial bank	$ 30,000
Expiration date of credit facility	Mar. 31, 2021
Borrowings outstanding under credit facility	$ 0		$ 0
Available borrowings under credit facility	30,000		$ 30,000
Notional balance	$ 60,000
Interest rate swap description	(i) notional reduction amounts and dates; (ii) LIBOR settlement rates; (iii) rate reset dates; and (iv) term/maturity.
Interest rate swap liability	$ 1,111
Magellan [Member]
Debt Instrument [Line Items]
Term loan				$ 60,000
Five - Year Term Loan [Member] | Magellan [Member]
Debt Instrument [Line Items]
Term loan		$ 60,000
Balloon principal payment	$ 37,500
Balloon principal payment repayment period	5 years