Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ 47,708	$ 49,141	$ 45,523	$ 38,690	$ 35,245	$ 36,054
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(5,274)		(5,257)
Retirement plan liability adjustment, net of tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(7,788)		(8,211)
Total accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ (13,062)	$ (12,970)	$ (13,468)	$ (12,809)	$ (12,928)	$ (13,309)