Segment Information - Sales by Contract Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue
Sales	$ 350,439	$ 382,679	$ 1,000,760	$ 1,025,277
Fixed Price
Disaggregation of Revenue
Sales	332,100	373,200	943,500	995,300
Other
Disaggregation of Revenue
Sales	18,300	9,500	57,300	30,000
Cubic Transportation Systems
Disaggregation of Revenue
Sales	215,500	212,700	601,800	595,200
Cubic Transportation Systems | Fixed Price
Disaggregation of Revenue
Sales	213,100	210,500	592,400	586,300
Cubic Transportation Systems | Other
Disaggregation of Revenue
Sales	2,400	2,200	9,400	8,900
Cubic Mission Solutions
Disaggregation of Revenue
Sales	69,000	95,000	167,200	203,300
Cubic Mission Solutions | Fixed Price
Disaggregation of Revenue
Sales	61,800	93,200	144,000	199,600
Cubic Mission Solutions | Other
Disaggregation of Revenue
Sales	7,200	1,800	23,200	3,700
Cubic Global Defense Systems
Disaggregation of Revenue
Sales	65,900	75,000	231,800	226,800
Cubic Global Defense Systems | Fixed Price
Disaggregation of Revenue
Sales	57,200	69,500	207,100	209,400
Cubic Global Defense Systems | Other
Disaggregation of Revenue
Sales	$ 8,700	$ 5,500	$ 24,700	$ 17,400