Segment Information - Revenue Recognition Method (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
Point in time
Disaggregation of Revenue
Sales	43,100	82,000	100,200	133,600
Over time
Disaggregation of Revenue
Sales	278,400	255,300	550,100	509,000
Cubic Transportation Systems
Disaggregation of Revenue
Sales	197,600	200,700	386,200	382,500
Cubic Transportation Systems | Point in time
Disaggregation of Revenue
Sales	28,100	21,800	45,800	38,500
Cubic Transportation Systems | Over time
Disaggregation of Revenue
Sales	169,500	178,900	340,400	344,000
Cubic Mission Solutions
Disaggregation of Revenue
Sales	39,500	61,900	98,200	108,300
Cubic Mission Solutions | Point in time
Disaggregation of Revenue
Sales	14,100	58,800	52,500	93,200
Cubic Mission Solutions | Over time
Disaggregation of Revenue
Sales	25,400	3,100	45,700	15,100
Cubic Global Defense Systems
Disaggregation of Revenue
Sales	84,400	74,700	165,900	151,800
Cubic Global Defense Systems | Point in time
Disaggregation of Revenue
Sales	900	1,400	1,900	1,900
Cubic Global Defense Systems | Over time
Disaggregation of Revenue
Sales	$ 83,500	$ 73,300	$ 164,000	$ 149,900