Business Segment Information - Sales by Deliverable 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
Products
Disaggregation of Revenue
Sales									947,765	1,011,069	704,941
Services
Disaggregation of Revenue
Sales									528,470	485,406	497,957
Cubic Transportation Systems
Disaggregation of Revenue
Sales									840,900	849,800	670,700
Cubic Transportation Systems | Products
Disaggregation of Revenue
Sales									459,700	496,900	288,100
Cubic Transportation Systems | Services
Disaggregation of Revenue
Sales									381,200	352,900	382,600
Cubic Mission Solutions
Disaggregation of Revenue
Sales									337,100	328,800	207,000
Cubic Mission Solutions | Products
Disaggregation of Revenue
Sales									301,800	301,000	187,500
Cubic Mission Solutions | Services
Disaggregation of Revenue
Sales									35,300	27,800	19,500
Cubic Global Defense Systems
Disaggregation of Revenue
Sales									298,200	317,900	325,200
Cubic Global Defense Systems | Products
Disaggregation of Revenue
Sales									186,300	213,200	229,300
Cubic Global Defense Systems | Services
Disaggregation of Revenue
Sales									$ 111,900	$ 104,700	$ 95,900