Segment Information - Sales by End Customer (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue
Sales	$ 328,839	$ 305,259
U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	175,500	169,000
Other
Disaggregation of Revenue
Sales	153,300	136,300
Cubic Transportation Systems
Disaggregation of Revenue
Sales	188,600	181,800
Cubic Transportation Systems | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	93,500	90,800
Cubic Transportation Systems | Other
Disaggregation of Revenue
Sales	95,100	91,000
Cubic Mission Solutions
Disaggregation of Revenue
Sales	58,700	46,400
Cubic Mission Solutions | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	55,200	45,800
Cubic Mission Solutions | Other
Disaggregation of Revenue
Sales	3,500	600
Cubic Global Defense Systems
Disaggregation of Revenue
Sales	81,500	77,100
Cubic Global Defense Systems | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	26,800	32,400
Cubic Global Defense Systems | Other
Disaggregation of Revenue
Sales	$ 54,700	$ 44,700