Segment Information - Sales by Contract Type (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue
Sales	$ 328,839	$ 305,259
Fixed Price
Disaggregation of Revenue
Sales	309,300	295,600
Other
Disaggregation of Revenue
Sales	19,500	9,700
Cubic Transportation Systems
Disaggregation of Revenue
Sales	188,600	181,800
Cubic Transportation Systems | Fixed Price
Disaggregation of Revenue
Sales	184,500	178,200
Cubic Transportation Systems | Other
Disaggregation of Revenue
Sales	4,100	3,600
Cubic Mission Solutions
Disaggregation of Revenue
Sales	58,700	46,400
Cubic Mission Solutions | Fixed Price
Disaggregation of Revenue
Sales	50,500	45,800
Cubic Mission Solutions | Other
Disaggregation of Revenue
Sales	8,200	600
Cubic Global Defense Systems
Disaggregation of Revenue
Sales	81,500	77,100
Cubic Global Defense Systems | Fixed Price
Disaggregation of Revenue
Sales	74,300	71,600
Cubic Global Defense Systems | Other
Disaggregation of Revenue
Sales	$ 7,200	$ 5,500