Postretirement Benefits - Net Periodic Pension Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Compensation and Retirement Disclosure [Abstract]
Service cost	$ 482	$ 406	$ 604
Interest cost	124	154	148
Expected return on assets	(210)	(214)	(247)
Amortization of losses	2	2	4
Other	0	0	160
Net periodic pension cost	398	348	669
Settlement loss	232	0	87
Total pension cost	$ 630	$ 348	$ 756