Segment Information - Revenue Recognition Method (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
Point in time
Disaggregation of Revenue
Sales	70,800	106,700	171,000	240,300
Over time
Disaggregation of Revenue
Sales	279,600	276,000	829,800	785,000
Cubic Transportation Systems
Disaggregation of Revenue
Sales	215,500	212,700	601,800	595,200
Cubic Transportation Systems | Point in time
Disaggregation of Revenue
Sales	26,500	29,700	72,300	68,200
Cubic Transportation Systems | Over time
Disaggregation of Revenue
Sales	189,000	183,000	529,500	527,000
Cubic Mission Solutions
Disaggregation of Revenue
Sales	69,000	95,000	167,200	203,300
Cubic Mission Solutions | Point in time
Disaggregation of Revenue
Sales	41,400	76,000	93,900	169,200
Cubic Mission Solutions | Over time
Disaggregation of Revenue
Sales	27,600	19,000	73,300	34,100
Cubic Global Defense Systems
Disaggregation of Revenue
Sales	65,900	75,000	231,800	226,800
Cubic Global Defense Systems | Point in time
Disaggregation of Revenue
Sales	2,900	1,000	4,800	2,900
Cubic Global Defense Systems | Over time
Disaggregation of Revenue
Sales	$ 63,000	$ 74,000	$ 227,000	$ 223,900