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, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Comprehensive Income (Loss)
Net income (loss)	$ 2,130	$ 713	$ (2,068)	$ (22,526)	$ (3,661)	$ (3,967)	$ (1,890)	$ (672)	$ (21,751)	$ (10,190)	$ 5,020
Other comprehensive income (loss), Pre-tax									39,879	64,931	(37,771)
Other comprehensive income (loss), Tax									(9,750)	(23,102)	11,201
Other comprehensive income (loss)									30,129	41,829	(26,570)
Comprehensive income (loss)									8,378	31,639	(21,550)
Pension and postretirement: Net gain (loss) arising during period
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									33,518	46,401	(18,299)
Other comprehensive income (loss), Tax									(7,576)	(17,095)	6,609
Other comprehensive income (loss)									25,942	29,306	(11,690)
Pension and postretirement: Less: amortization of prior service cost
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									374	808	(808)
Other comprehensive income (loss), Tax									(99)	(298)	299
Other comprehensive income (loss)									275	510	(509)
Pension and postretirement: Less: amortization of gain (loss)
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									7,887	15,517	(11,663)
Other comprehensive income (loss), Tax									(2,075)	(5,709)	4,293
Other comprehensive income (loss)									5,812	9,808	(7,370)
Accumulated Translation Adjustment
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									(1,900)	2,205	(7,001)
Other comprehensive income (loss)									$ (1,900)	$ 2,205	$ (7,001)