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, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Comprehensive Income (Loss)
Net income (loss)	$ 6,037	$ 3,802	$ 1,509	$ (1,603)	$ 2,130	$ 713	$ (2,068)	$ (22,526)	$ 9,745	$ (21,751)	$ (10,190)
Other comprehensive income (loss), Pre-tax									(48,509)	39,879	64,931
Other comprehensive income (loss), Tax									10,436	(9,750)	(23,102)
Other comprehensive income (loss)									(38,073)	30,129	41,829
Comprehensive income (loss)									(28,328)	8,378	31,639
Pension and postretirement: Net gain (loss) arising during period
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									(48,052)	33,518	46,401
Other comprehensive income (loss), Tax									11,266	(7,576)	(17,095)
Other comprehensive income (loss)									(36,786)	25,942	29,306
Pension and postretirement: Less: amortization of prior service cost
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									228	374	808
Other comprehensive income (loss), Tax									(58)	(99)	(298)
Other comprehensive income (loss)									170	275	510
Pension and postretirement: Less: amortization of gain (loss)
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									2,935	7,887	15,517
Other comprehensive income (loss), Tax									(772)	(2,075)	(5,709)
Other comprehensive income (loss)									2,163	5,812	9,808
Accumulated Translation Adjustment
Comprehensive Income (Loss)
Other comprehensive income (loss), Pre-tax									(3,620)	(1,900)	2,205
Other comprehensive income (loss)									$ (3,620)	$ (1,900)	$ 2,205