Segment Information - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenue recognition
Increase (decrease) in operating income	$ (1,697)	$ 13,893	$ (7,870)	$ (3,270)
Net income (loss)	$ (21,957)	$ 4,498	$ (24,364)	$ 9,228
Increase (decrease) in net income per common share (in dollars per share)	$ (0.81)	$ 0.17	$ (0.90)	$ 0.34
Sales	$ 361,869	$ 375,240	$ 1,040,255	$ 1,055,077
Defense Systems
Revenue recognition
Increase (decrease) in operating income	8,900	900	4,000	(23,700)
Sales	129,800	119,000	350,700	331,300
Defense Systems | Littoral Combat Ship Virtual Training Contract
Revenue recognition
Increase (decrease) in operating income	8,000
Sales	8,000
Unallocated corporate expenses and other
Revenue recognition
Expense related to the development of ERP system	8,900	8,500	23,600	24,400
Increase (decrease) in operating income	(12,900)	(12,300)	(33,300)	(32,800)
Change in estimated total costs | Adjustment
Revenue recognition
Increase (decrease) in operating income	6,100	200	(1,200)	(3,100)
Net income (loss)	$ 3,200	$ 100	$ (1,000)	$ (1,800)
Increase (decrease) in net income per common share (in dollars per share)	$ 0.12	$ 0.00	$ (0.04)	$ (0.07)