Comprehensive Income (Loss) and Changes in Accumulated Other Comprehensive Income (Loss) by Component - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Accumulated other comprehensive income (loss)
Balance	$ 341,989	$ 346,730	$ 355,803
Other comprehensive loss	(26,570)	(26,125)	(5,029)
Balance	311,299	341,989	346,730
AOCI Attributable to Parent
Accumulated other comprehensive income (loss)
Balance	(87,953)	(61,828)	(56,799)
Other comprehensive loss before reclassifications	(34,449)	(31,163)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(4,592)	(2,930)
Other comprehensive loss	(26,570)	(26,125)	(5,029)
Balance	(114,523)	(87,953)	(61,828)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Balance	(62,985)	(42,800)
Other comprehensive loss before reclassifications	(17,855)	(23,688)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(3,548)	(2,031)
Other comprehensive loss	(11,757)	(20,185)
Balance	(74,742)	(62,985)	(42,800)
Accumulated Defined Benefit Plans Adjustment | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Balance	(21,773)	(20,000)
Other comprehensive loss before reclassifications	(9,593)	(3,308)
Amounts reclassified from accumulated other comprehensive income (loss), Tax benefit	(1,044)	(899)
Other comprehensive loss	(7,812)	(1,773)
Balance	(29,585)	(21,773)	(20,000)
Pension and postretirement: Less: amortization of prior service cost
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	808	808
Other comprehensive loss	(509)	(510)	1,314
Pension and postretirement: Less: amortization of prior service cost | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	808	808
Pension and postretirement: Less: amortization of gain (loss)
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	11,663	7,160
Other comprehensive loss	(7,370)	(4,528)	(4,164)
Pension and postretirement: Less: amortization of gain (loss) | Defined Benefit Pension Plans
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	8,838	4,726
Pension and postretirement: Less: amortization of gain (loss) | Postretirement Health Care Benefits
Accumulated other comprehensive income (loss)
Amounts reclassified from accumulated other comprehensive income (loss), before tax	2,825	2,434
Accumulated Translation Adjustment
Accumulated other comprehensive income (loss)
Balance	(3,195)	972
Other comprehensive loss before reclassifications	(7,001)	(4,167)
Other comprehensive loss	(7,001)	(4,167)	(991)
Balance	$ (10,196)	$ (3,195)	$ 972