Business Segment Information - Sales by Contract Type (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue
Sales	$ 475,475	$ 350,439	$ 321,482	$ 328,839	$ 471,198	$ 382,679	$ 337,339	$ 305,259	$ 1,476,235	$ 1,496,475	$ 1,202,898
Fixed Price
Disaggregation of Revenue
Sales									1,397,900	1,452,400	1,146,200
Other
Disaggregation of Revenue
Sales									78,300	44,100	56,700
Cubic Transportation Systems
Disaggregation of Revenue
Sales									840,900	849,800	670,700
Cubic Transportation Systems | Fixed Price
Disaggregation of Revenue
Sales									828,600	838,100	653,800
Cubic Transportation Systems | Other
Disaggregation of Revenue
Sales									12,300	11,700	16,900
Cubic Mission Solutions
Disaggregation of Revenue
Sales									337,100	328,800	207,000
Cubic Mission Solutions | Fixed Price
Disaggregation of Revenue
Sales									305,000	321,500	206,100
Cubic Mission Solutions | Other
Disaggregation of Revenue
Sales									32,100	7,300	900
Cubic Global Defense Systems
Disaggregation of Revenue
Sales									298,200	317,900	325,200
Cubic Global Defense Systems | Fixed Price
Disaggregation of Revenue
Sales									264,300	292,800	286,300
Cubic Global Defense Systems | Other
Disaggregation of Revenue
Sales									$ 33,900	$ 25,100	$ 38,900