Segment Information - Sales by End Customer (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue
Sales	$ 321,482	$ 337,339	$ 650,321	$ 642,598
U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	165,200	192,400	340,700	361,400
Other
Disaggregation of Revenue
Sales	156,300	144,900	309,600	281,200
Cubic Transportation Systems
Disaggregation of Revenue
Sales	197,600	200,700	386,200	382,500
Cubic Transportation Systems | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	104,000	96,700	197,500	187,500
Cubic Transportation Systems | Other
Disaggregation of Revenue
Sales	93,600	104,000	188,700	195,000
Cubic Mission Solutions
Disaggregation of Revenue
Sales	39,500	61,900	98,200	108,300
Cubic Mission Solutions | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	35,000	58,100	90,200	103,900
Cubic Mission Solutions | Other
Disaggregation of Revenue
Sales	4,500	3,800	8,000	4,400
Cubic Global Defense Systems
Disaggregation of Revenue
Sales	84,400	74,700	165,900	151,800
Cubic Global Defense Systems | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Sales	26,200	37,600	53,000	70,000
Cubic Global Defense Systems | Other
Disaggregation of Revenue
Sales	$ 58,200	$ 37,100	$ 112,900	$ 81,800