Changes in Accumulated Other Comprehensive Income (Loss) by Component - Other (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Accumulated other comprehensive income (loss)
Balance	$ 297,891	$ 303,626	$ 301,501	$ 296,275
Other comprehensive income (loss)	1,259	(2,198)	7,637	3,764
Balance	293,891	303,612	293,891	303,612
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss)
Balance	(68,223)	(87,959)	(74,601)	(80,638)
Other comprehensive income (loss) before reclassifications	(268)	(3,918)	4,582	325
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(464)	(617)	(927)	(1,231)
Other comprehensive income (loss)	1,259	(2,198)	7,637	3,764
Balance	(66,964)	(90,157)	(66,964)	(90,157)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Balance	(63,865)	(60,942)	(65,393)	(53,811)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(464)	(494)	(927)	(987)
Other comprehensive income (loss)	1,527	1,380	3,055	2,758
Balance	(62,338)	(59,562)	(62,338)	(59,562)
Accumulated Defined Benefit Plans Adjustment | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Balance	613	(17,749)	613	(13,316)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit		(123)		(244)
Other comprehensive income (loss)		340		681
Balance	613	(17,409)	613	(17,409)
Amortization of Pension and Postretirement Plan items
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	52	52	103	103
Amortization of Pension and Postretirement Plan items | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	52	52	103	103
Actuarial losses
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	1,939	2,285	3,879	4,567
Actuarial losses | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	1,939	1,822	3,879	3,642
Actuarial losses | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax		463		925
Accumulated Translation Adjustment
Accumulated other comprehensive income (loss)
Balance	(4,971)	(9,268)	(9,821)	(13,511)
Other comprehensive income (loss) before reclassifications	(268)	(3,918)	4,582	325
Other comprehensive income (loss)	(268)	(3,918)	4,582	325
Balance	$ (5,239)	$ (13,186)	$ (5,239)	(13,186)
ASU 2018-02 | Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss)				(13,283)
ASU 2018-02 | Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss)				(8,509)
ASU 2018-02 | Accumulated Defined Benefit Plans Adjustment | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss)				$ (4,774)