Comprehensive Income (Loss) and Changes in Accumulated Other Comprehensive Income (Loss) by Component - Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Comprehensive Income (Loss)
Net income (loss)	$ 41,975	$ 45,087	$ (8,683)
Other comprehensive income (loss), Pre-tax	20,691	5,173	80,158
Other comprehensive income (loss), Tax	(3,226)	(3,924)	(17,898)
Other comprehensive income (loss)	17,465	1,249	62,260
Comprehensive income	59,440	46,336	53,577
Pension and postretirement: Net gain (loss) arising during period
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax	16,008	16,991	68,941
Other comprehensive income (loss), Tax	(3,700)	(3,924)	(16,044)
Other comprehensive income (loss)	12,308	13,067	52,897
Pension and postretirement: Less: amortization of prior service cost
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax	233	239	228
Other comprehensive income (loss), Tax	(55)	(56)	(52)
Other comprehensive income (loss)	178	183	176
Pension and postretirement: Less: amortization of gain (loss)
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax	(2,279)	(240)	7,735
Other comprehensive income (loss), Tax	529	56	(1,802)
Other comprehensive income (loss)	(1,750)	(184)	5,933
Accumulated Translation Adjustment
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax	6,729	(11,817)	3,254
Other comprehensive income (loss)	$ 6,729	$ (11,817)	$ 3,254