Postretirement Benefits - Funded Status and Amounts Recognized in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of fiscal year	$ 7,661	$ 8,213
Service cost	548	482	$ 406
Interest cost	71	124	154
Actuarial loss	106	733
Benefits paid	(712)	(209)
Employee contributions	156	444
Settlements paid	0	(1,795)
Curtailment gain	(1,064)	0
Foreign currency translation	81	(331)
Benefit obligation at end of fiscal year	6,847	7,661	8,213
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of assets at beginning of fiscal year	4,838	6,131
Actual return on plan assets	30	112
Disbursements	(837)	(334)
Employer contributions	296	306
Employee contributions	352	642
Settlements paid	0	(1,795)
Foreign currency translation	55	(224)
Fair value of assets at end of fiscal year	4,734	4,838	$ 6,131
Accrued benefit obligation	$ 2,113	$ 2,823