Summary of Significant Accounting Policies - Reclassification Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before taxes	$ (8,207)	$ (7,531)
Income tax expense	(701)	(361)
Net loss	(7,506)	(7,170)
Reclassification out of Accumulated Other Comprehensive Income | Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before taxes	0	0
Reclassification out of Accumulated Other Comprehensive Income | Net actuarial gain (loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before taxes	(4,214)	974
Reclassification out of Accumulated Other Comprehensive Income | Settlements/curtailments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before taxes	246	0
Reclassification out of Accumulated Other Comprehensive Income | Retirement Plan Liability Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before taxes	(3,968)	974
Income tax expense	0	0
Net loss	$ (3,968)	$ 974