Restructuring Costs - Restructuring Charges (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Restructuring plan
Restructuring costs	$ 7,746	$ 3,807	$ 11,881	$ 5,382
Unallocated corporate expenses
Restructuring plan
Restructuring costs	5,400	3,200	6,200	4,300
Cubic Transportation Systems
Restructuring plan
Restructuring costs	1,600	100	1,800	500
Cubic Mission and Performance Solutions
Restructuring plan
Restructuring costs	$ 800	$ 500	$ 3,900	$ 600