Segment Information - Sales by End Customer (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
U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	225,100	252,300	565,900	613,600
Other
Disaggregation of Revenue
Sales	125,300	130,400	434,900	411,700
Cubic Transportation Systems
Disaggregation of Revenue
Sales	215,500	212,700	601,800	595,200
Cubic Transportation Systems | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	127,800	123,100	325,400	310,700
Cubic Transportation Systems | Other
Disaggregation of Revenue
Sales	87,700	89,600	276,400	284,500
Cubic Mission Solutions
Disaggregation of Revenue
Sales	69,000	95,000	167,200	203,300
Cubic Mission Solutions | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	64,900	91,800	155,100	195,600
Cubic Mission Solutions | Other
Disaggregation of Revenue
Sales	4,100	3,200	12,100	7,700
Cubic Global Defense Systems
Disaggregation of Revenue
Sales	65,900	75,000	231,800	226,800
Cubic Global Defense Systems | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	32,400	37,400	85,400	107,300
Cubic Global Defense Systems | Other
Disaggregation of Revenue
Sales	$ 33,500	$ 37,600	$ 146,400	$ 119,500