Summary of Significant Accounting Policies - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ 36,054	$ 36,054	$ 45,523	$ 36,054
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	36,054	44,189
Other comprehensive income (loss) before reclassifications	(1,150)	(5,355)
Amounts reclassified from accumulated other comprehensive income	991	675
Net current-period other comprehensive income (loss)	(159)	(4,680)
Ending balance	45,523	36,054
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(5,257)	(4,955)	(5,257)	(5,667)
AOCI tax benefit			0	0
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,667)	(4,955)
Other comprehensive income (loss) before reclassifications	410	(712)
Amounts reclassified from accumulated other comprehensive income	0	0
Net current-period other comprehensive income (loss)	410	(712)
Ending balance	(5,257)	(5,667)
Retirement Plan Liability Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(8,211)	(7,642)	(8,211)	(7,642)
AOCI tax benefit			(3,758)	(3,758)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(7,642)	(3,674)
Other comprehensive income (loss) before reclassifications	(1,560)	(4,643)
Amounts reclassified from accumulated other comprehensive income	991	675
Net current-period other comprehensive income (loss)	(569)	(3,968)
Ending balance	(8,211)	(7,642)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(13,309)	(8,629)	$ (13,468)	$ (13,309)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(13,309)	(8,629)
Ending balance	$ (13,468)	$ (13,309)