Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated other comprehensive income (loss)
Balance	$ 303,612	$ 329,692	$ 296,275	$ 333,220
Other comprehensive income (loss)	1,543	(1,223)	5,307	(204)
Balance	295,124	330,140	295,124	330,140
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss)
Balance	(90,157)	(41,546)	(80,638)	(42,565)
Other comprehensive income (loss) before reclassifications	(176)	(1,803)	149	(1,943)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(612)	(207)	(1,843)	(621)
Other comprehensive income (loss)	1,543	(1,223)	5,307	(204)
Balance	(88,614)	(42,769)	(88,614)	(42,769)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Balance	(59,562)	(20,860)	(53,811)	(21,473)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(489)	(108)	(1,476)	(325)
Other comprehensive income (loss)	1,381	307	4,139	920
Balance	(58,181)	(20,553)	(58,181)	(20,553)
Accumulated Defined Benefit Plans Adjustment | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Balance	(17,409)	(10,655)	(13,316)	(11,201)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(123)	(99)	(367)	(296)
Other comprehensive income (loss)	338	273	1,019	819
Balance	(17,071)	(10,382)	(17,071)	(10,382)
Amortization of Pension and Postretirement Plan items
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	51	51	154	154
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	51	51	154	154
Actuarial losses
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	2,280	736	6,847	2,206
Actuarial losses | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	1,819	364	5,461	1,091
Actuarial losses | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	461	372	1,386	1,115
Accumulated Translation Adjustment
Accumulated other comprehensive income (loss)
Balance	(13,186)	(10,031)	(13,511)	(9,891)
Other comprehensive income (loss) before reclassifications	(176)	(1,803)	149	(1,943)
Other comprehensive income (loss)	(176)	(1,803)	149	(1,943)
Balance	$ (13,362)	$ (11,834)	(13,362)	$ (11,834)
Reclassifications out of accumulated other comprehensive income | Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax			(13,283)
Reclassifications out of accumulated other comprehensive income | Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax			(8,509)
Reclassifications out of accumulated other comprehensive income | Accumulated Defined Benefit Plans Adjustment | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax			$ (4,774)