Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Accumulated other comprehensive income (loss)
Balance			$ 311,299
Other comprehensive income (loss)	$ 3,414	$ 1,498	2,968	$ 1,786
Balance	307,159		307,159
AOCI Attributable to Parent
Accumulated other comprehensive income (loss)
Balance	(114,969)	(87,665)	(114,523)	(87,953)
Other comprehensive income (loss) before reclassifications	835	(478)	(2,191)	(2,166)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(1,502)	(1,149)	(3,004)	(2,299)
Other comprehensive income (loss)	3,414	1,498	2,968	1,786
Balance	(111,555)	(86,167)	(111,555)	(86,167)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Balance	(72,838)	(61,455)	(74,742)	(62,985)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(1,109)	(890)	(2,217)	(1,780)
Other comprehensive income (loss)	1,903	1,529	3,807	3,059
Balance	(70,935)	(59,926)	(70,935)	(59,926)
Accumulated Defined Benefit Plans Adjustment | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Balance	(28,909)	(21,327)	(29,585)	(21,773)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(393)	(259)	(787)	(519)
Other comprehensive income (loss)	676	447	1,352	893
Balance	(28,233)	(20,880)	(28,233)	(20,880)
Amortization of Pension and Postretirement Plan items
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	202	202	404	404
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	404	404
Actuarial losses
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	3,879	2,923	7,759	5,847
Actuarial losses | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	2,810	2,217	5,620	4,435
Actuarial losses | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	1,069	706	2,139	1,412
Accumulated Translation Adjustment
Accumulated other comprehensive income (loss)
Balance	(13,222)	(4,883)	(10,196)	(3,195)
Other comprehensive income (loss) before reclassifications	835	(478)	(2,191)	(2,166)
Other comprehensive income (loss)	835	(478)	(2,191)	(2,166)
Balance	$ (12,387)	$ (5,361)	$ (12,387)	$ (5,361)