Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Accumulated other comprehensive income (loss)
Balance			$ 341,989
Net current-period other comprehensive income (loss)	$ 1,498	$ (1,533)	1,786	$ (2,738)
Balance	338,115		338,115
AOCI Attributable to Parent
Accumulated other comprehensive income (loss)
Balance	(87,665)	(63,033)	(87,953)	(61,828)
Other comprehensive income (loss) before classifications	(478)	(2,786)	(2,166)	(5,245)
Amounts reclassified from accumulated other comprehensive income (loss), Tax expense or (benefit)	(1,149)	(739)	(2,299)	(1,477)
Net current-period other comprehensive income (loss)	1,498	(1,533)	1,786	(2,738)
Balance	(86,167)	(64,566)	(86,167)	(64,566)
Defined Benefit Plans | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Balance	(61,455)	(41,928)	(62,985)	(42,800)
Amounts reclassified from accumulated other comprehensive income (loss), Tax expense or (benefit)	(890)	(512)	(1,780)	(1,025)
Net current-period other comprehensive income (loss)	1,529	870	3,059	1,742
Balance	(59,926)	(41,058)	(59,926)	(41,058)
Defined Benefit Plans | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Balance	(21,327)	(19,618)	(21,773)	(20,000)
Amounts reclassified from accumulated other comprehensive income (loss), Tax expense or (benefit)	(259)	(227)	(519)	(452)
Net current-period other comprehensive income (loss)	447	383	893	765
Balance	(20,880)	(19,235)	(20,880)	(19,235)
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	2,923	1,790	5,847	3,580
Actuarial losses | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	2,217	1,180	4,435	2,363
Actuarial losses | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	706	610	1,412	1,217
Foreign Exchange
Accumulated other comprehensive income (loss)
Balance	(4,883)	(1,487)	(3,195)	972
Other comprehensive income (loss) before classifications	(478)	(2,786)	(2,166)	(5,245)
Net current-period other comprehensive income (loss)	(478)	(2,786)	(2,166)	(5,245)
Balance	$ (5,361)	$ (4,273)	$ (5,361)	$ (4,273)