Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Accumulated other comprehensive income (loss)
Balance	$ 333,220	$ 333,772	$ 311,299
Other comprehensive income (loss)	(38,073)	30,129	41,829
Balance	296,275	333,220	333,772
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss)
Balance	(42,565)	(72,694)	(114,523)
Other comprehensive income (loss) before reclassifications	(40,407)	24,042
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(830)	(2,174)
Other comprehensive income (loss)	(38,073)	30,129	41,829
Balance	(80,638)	(42,565)	(72,694)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Balance	(21,473)	(43,012)
Other comprehensive income (loss) before reclassifications	(33,578)	17,658
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(437)	(1,381)
Other comprehensive income (loss)	(32,338)	21,539
Balance	(53,811)	(21,473)	(43,012)
Accumulated Defined Benefit Plans Adjustment | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Balance	(11,201)	(21,691)
Other comprehensive income (loss) before reclassifications	(3,209)	8,284
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(393)	(793)
Other comprehensive income (loss)	(2,115)	10,490
Balance	(13,316)	(11,201)	(21,691)
Pension and postretirement: Less: amortization of prior service cost
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	228	374
Other comprehensive income (loss)	170	275	510
Pension and postretirement: Less: amortization of prior service cost | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	228	374
Pension and postretirement: Less: amortization of gain (loss)
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	2,936	7,887
Other comprehensive income (loss)	2,163	5,812	9,808
Pension and postretirement: Less: amortization of gain (loss) | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	1,449	4,888
Pension and postretirement: Less: amortization of gain (loss) | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	1,487	2,999
Accumulated Translation Adjustment
Accumulated other comprehensive income (loss)
Balance	(9,891)	(7,991)
Other comprehensive income (loss) before reclassifications	(3,620)	(1,900)
Other comprehensive income (loss)	(3,620)	(1,900)	2,205
Balance	$ (13,511)	$ (9,891)	$ (7,991)