Summary of Significant Accounting Policies - Reclassification Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016
Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified from accumulated other comprehensive loss, before taxes	[1]	$ 15	$ 0
Net actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified from accumulated other comprehensive loss, before taxes	[1]	927	828
Settlements/curtailments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified from accumulated other comprehensive loss, before taxes	[1]	(48)	223
Retirement Plan Liability Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified from accumulated other comprehensive loss, before taxes		894	1,051
Income tax expense		0	0
Net of taxes		$ 894	$ 1,051

[1] These accumulated other comprehensive income components are included in the computation of net periodic benefit cost. See Note 7, Retirement Benefit Plans, of the consolidated financial statements for further information.