Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Accumulated other comprehensive income (loss)
Balance	$ 328,624	$ 310,687	$ 333,220	$ 333,772
Other comprehensive income (loss)	1,610	3,626	1,019	5,449
Balance	329,692	310,205	329,692	310,205
Accumulated Other Comprehensive Income (Loss)
Accumulated other comprehensive income (loss)
Balance	(43,156)	(70,871)	(42,565)	(72,694)
Other comprehensive income (loss) before reclassifications	1,031	2,316	(140)	2,833
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(207)	(755)	(414)	(1,515)
Other comprehensive income (loss)	1,610	3,626	1,019	5,449
Balance	(41,546)	(67,245)	(41,546)	(67,245)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Balance	(21,166)	(42,180)	(21,473)	(43,012)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(109)	(477)	(217)	(961)
Other comprehensive income (loss)	306	838	613	1,670
Balance	(20,860)	(41,342)	(20,860)	(41,342)
Accumulated Defined Benefit Plans Adjustment | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Balance	(10,928)	(21,217)	(11,201)	(21,691)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(98)	(278)	(197)	(554)
Other comprehensive income (loss)	273	472	546	946
Balance	(10,655)	(20,745)	(10,655)	(20,745)
Amortization of Pension and Postretirement Plan items
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	52	94	103	187
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	94	103	187
Actuarial losses
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	734	1,971	1,470	3,944
Actuarial losses | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	363	1,221	727	2,444
Actuarial losses | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	371	750	743	1,500
Accumulated Translation Adjustment
Accumulated other comprehensive income (loss)
Balance	(11,062)	(7,474)	(9,891)	(7,991)
Other comprehensive income (loss) before reclassifications	1,031	2,316	(140)	2,833
Other comprehensive income (loss)	1,031	2,316	(140)	2,833
Balance	$ (10,031)	$ (5,158)	$ (10,031)	$ (5,158)