Changes in Accumulated Other Comprehensive Income (Loss) by Component - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accumulated other comprehensive income (loss)
Balance	$ 333,772
Other comprehensive income (loss)	1,823	$ (446)
Balance	310,687
AOCI Attributable to Parent
Accumulated other comprehensive income (loss)
Balance	(72,694)	(114,523)
Other comprehensive income (loss) before reclassifications	517	(3,026)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(760)	(1,502)
Other comprehensive income (loss)	1,823	(446)
Balance	(70,871)	(114,969)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Balance	(43,012)	(74,742)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(484)	(1,108)
Other comprehensive income (loss)	832	1,904
Balance	(42,180)	(72,838)
Accumulated Defined Benefit Plans Adjustment | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Balance	(21,691)	(29,585)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(276)	(394)
Other comprehensive income (loss)	474	676
Balance	(21,217)	(28,909)
Amortization of Pension and Postretirement Plan items
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	93	202
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	93	202
Actuarial losses
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	1,973	3,880
Actuarial losses | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	1,223	2,810
Actuarial losses | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	750	1,070
Accumulated Translation Adjustment
Accumulated other comprehensive income (loss)
Balance	(7,991)	(10,196)
Other comprehensive income (loss) before reclassifications	517	(3,026)
Other comprehensive income (loss)	517	(3,026)
Balance	$ (7,474)	$ (13,222)