Business Segment Information - Narrative (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($) item $ / shares
Revenue recognition
Increase (decrease) in operating income	$ 27,673	$ 10,290	$ (1,679)	$ (11,902)	$ 21,207	$ (6,872)	$ (6,084)	$ (5,623)	$ 24,382	$ 2,628	$ (11,649)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest									$ 12,036	$ (11,209)	$ 1,735
Increase (decrease) in net income per common share (in dollars per share) | $ / shares	$ 0.65	$ 0.23	$ (0.07)	$ (0.36)	$ 0.49	$ (0.81)	$ 0.02	$ (0.11)	$ 0.45	$ (0.41)	$ 0.06
Restructuring costs									$ 5,018	$ 2,260	$ 1,278
Cubic Global Defense
Revenue recognition
Increase (decrease) in operating income									16,600	28,100	19,900
Restructuring costs									1,300	900	300
Transportation Systems
Revenue recognition
Increase (decrease) in operating income									60,400	39,800	57,500
Restructuring costs									400	400	$ 1,000
Reduction in employee headcount | item											20
Cubic Mission Solutions
Revenue recognition
Increase (decrease) in operating income									(100)	(9,300)	$ (37,000)
Restructuring costs									200
Unallocated corporate expenses and other
Revenue recognition
Increase (decrease) in operating income									(52,500)	(56,000)	(52,000)
Restructuring costs									3,100	1,000
Change in estimated total costs | Adjustment
Revenue recognition
Increase (decrease) in operating income	$ (4,200)				$ (1,600)				(7,000)	5,700	(900)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ (3,100)				$ (1,100)				$ (5,100)	$ 3,200	$ (500)
Increase (decrease) in net income per common share (in dollars per share) | $ / shares	$ (0.12)				$ (0.04)				$ (0.19)	$ 0.12	$ (0.02)