Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated other comprehensive income (loss)
Balance			$ 311,299
Other comprehensive income (loss)	$ 5,222	$ (1,769)	8,190	$ 17
Balance	305,998		305,998
AOCI Attributable to Parent
Accumulated other comprehensive income (loss)
Balance	(111,555)	(86,167)	(114,523)	(87,953)
Other comprehensive income (loss) before reclassifications	2,642	(3,745)	451	(5,911)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(1,501)	(1,151)	(4,505)	(3,450)
Other comprehensive income (loss)	5,222	(1,769)	8,190	17
Balance	(106,333)	(87,936)	(106,333)	(87,936)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Balance	(70,935)	(59,926)	(74,742)	(62,985)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(1,107)	(891)	(3,324)	(2,671)
Other comprehensive income (loss)	1,904	1,529	5,711	4,588
Balance	(69,031)	(58,397)	(69,031)	(58,397)
Accumulated Defined Benefit Plans Adjustment | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Balance	(28,233)	(20,880)	(29,585)	(21,773)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(394)	(260)	(1,181)	(779)
Other comprehensive income (loss)	676	447	2,028	1,340
Balance	(27,557)	(20,433)	(27,557)	(20,433)
Amortization of Pension and Postretirement Plan items
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	202	202	606	606
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	202	202	606	606
Actuarial losses
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	3,879	2,925	11,638	8,772
Actuarial losses | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	2,809	2,218	8,429	6,653
Actuarial losses | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	1,070	707	3,209	2,119
Accumulated Translation Adjustment
Accumulated other comprehensive income (loss)
Balance	(12,387)	(5,361)	(10,196)	(3,195)
Other comprehensive income (loss) before reclassifications	2,642	(3,745)	451	(5,911)
Other comprehensive income (loss)	2,642	(3,745)	451	(5,911)
Balance	$ (9,745)	$ (9,106)	$ (9,745)	$ (9,106)