Business Segment Information - Restructuring liability and employee separation expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Restructuring liability
Balance as of the beginning of the period	$ 975	$ 553
Accrued costs	5,018	2,260	$ 1,278
Cash payments	(5,058)	(1,838)
Balance as of the end of the period	$ 935	$ 975	$ 553