Other Comprehensive Loss Gains (losses) in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), ending balance	$ 480,144
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	(2,705)	$ (4,212)	$ (739)
Other comprehensive (loss) income before reclassifications	(2,830)	1,507	(3,473)
Amounts (loss) reclassified from accumulated other comprehensive loss into earnings	0	0	0
Accumulated other comprehensive income (loss), ending balance	(5,535)	(2,705)	(4,212)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	(10,475)	(4,907)	(5,373)
Other comprehensive (loss) income before reclassifications	(927)	(5,939)	167
Amounts (loss) reclassified from accumulated other comprehensive loss into earnings	1,006	371	299
Accumulated other comprehensive income (loss), ending balance	(10,396)	(10,475)	(4,907)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	176	102	123
Other comprehensive (loss) income before reclassifications	(5,375)	(424)	(118)
Amounts (loss) reclassified from accumulated other comprehensive loss into earnings	658	498	97
Accumulated other comprehensive income (loss), ending balance	$ (4,541)	$ 176	$ 102