Segment Information - Sales by Deliverable Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue
Sales	$ 343,408	$ 321,482	$ 662,202	$ 650,321
Products
Disaggregation of Revenue
Sales	200,428	187,494	381,917	388,098
Services
Disaggregation of Revenue
Sales	142,980	133,988	280,285	262,223
Cubic Transportation Systems
Disaggregation of Revenue
Sales	217,400	197,600	414,500	386,200
Cubic Transportation Systems | Products
Disaggregation of Revenue
Sales	113,100	99,700	213,200	193,100
Cubic Transportation Systems | Services
Disaggregation of Revenue
Sales	104,300	97,900	201,300	193,100
Cubic Mission and Performance Solutions
Disaggregation of Revenue
Sales	126,000	123,900	247,700	264,100
Cubic Mission and Performance Solutions | Products
Disaggregation of Revenue
Sales	87,300	87,800	168,700	195,000
Cubic Mission and Performance Solutions | Services
Disaggregation of Revenue
Sales	$ 38,700	$ 36,100	$ 79,000	$ 69,100