Comprehensive Income (Loss) and Changes in Accumulated Other Comprehensive Income (Loss) by Component - Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Comprehensive Income (Loss)
Net loss	$ (3,661)	$ (3,967)	$ (1,890)	$ (672)	$ 3,162	$ 2,792	$ (1,162)	$ 228	$ (10,190)	$ 5,020	$ 30,486
Other comprehensive income (loss), Pre-tax									64,931	(37,771)	(38,650)
Other comprehensive income (loss), Tax									(23,102)	11,201	12,525
Other comprehensive income (loss)									41,829	(26,570)	(26,125)
Comprehensive income (loss)									31,639	(21,550)	4,361
Pension and postretirement: Net gain (loss) arising during period
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									46,401	(18,299)	(26,515)
Other comprehensive income (loss), Tax									(17,095)	6,609	9,595
Other comprehensive income (loss)									29,306	(11,690)	(16,920)
Pension and postretirement: Less: amortization of prior service cost
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									808	(808)	(808)
Other comprehensive income (loss), Tax									(298)	299	298
Other comprehensive income (loss)									510	(509)	(510)
Pension and postretirement: Less: amortization of gain (loss)
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									15,517	(11,663)	(7,160)
Other comprehensive income (loss), Tax									(5,709)	4,293	2,632
Other comprehensive income (loss)									9,808	(7,370)	(4,528)
Accumulated Translation Adjustment
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									2,205	(7,001)	(4,167)
Other comprehensive income (loss)									$ 2,205	$ (7,001)	$ (4,167)