Other Comprehensive Loss Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Oct. 01, 2019	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ 482,063	$ 365,822	$ 364,485	$ 362,016	$ 216,575
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(5,535)	(2,705)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(10,396)	(10,475)
Other comprehensive income (loss), tax expense (benefit)	839	776
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(4,541)	176
Other comprehensive income (loss), tax expense (benefit)	135	135
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ (20,472)	$ (13,004)		$ (9,017)	$ (5,989)