Summary of Significant Accounting Policies - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ 49,622	$ 45,523
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	45,523	36,054
Other comprehensive income (loss) before reclassifications	3,269	(1,150)
Amounts reclassified from accumulated other comprehensive loss	1,120	991
Net current-period other comprehensive income (loss)	4,389	(159)
Ending balance	49,622	45,523
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(5,359)	(5,257)
AOCI tax benefit	0	0
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,257)	(5,667)
Other comprehensive income (loss) before reclassifications	(102)	410
Amounts reclassified from accumulated other comprehensive loss	0	0
Net current-period other comprehensive income (loss)	(102)	410
Ending balance	(5,359)	(5,257)
Retirement Plan Liability Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(3,720)	(8,211)
AOCI tax benefit	(3,758)	(3,758)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(8,211)	(7,642)
Other comprehensive income (loss) before reclassifications	3,371	(1,560)
Amounts reclassified from accumulated other comprehensive loss	1,120	991
Net current-period other comprehensive income (loss)	4,491	(569)
Ending balance	(3,720)	(8,211)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(9,079)	(13,468)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(13,468)	(13,309)
Ending balance	$ (9,079)	$ (13,468)