Postretirement Benefits - Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of fiscal year	$ 6,847	$ 7,661
Service cost	270	548	$ 482
Interest cost	27	71	124
Actuarial loss	(617)	106
Benefits paid		(712)
Employee contributions		156
Settlements paid	(2,526)
Curtailment gain		(1,064)
Foreign currency translation	(29)	81
Benefit obligation at end of fiscal year	$ 3,972	$ 6,847	$ 7,661