Segment Information - Sales by Contract Type (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
Fixed Price
Disaggregation of Revenue
Sales	302,100	326,300	611,400	621,900
Other
Disaggregation of Revenue
Sales	19,400	11,000	38,900	20,700
Cubic Transportation Systems
Disaggregation of Revenue
Sales	197,600	200,700	386,200	382,500
Cubic Transportation Systems | Fixed Price
Disaggregation of Revenue
Sales	194,800	197,500	379,300	375,700
Cubic Transportation Systems | Other
Disaggregation of Revenue
Sales	2,800	3,200	6,900	6,800
Cubic Mission Solutions
Disaggregation of Revenue
Sales	39,500	61,900	98,200	108,300
Cubic Mission Solutions | Fixed Price
Disaggregation of Revenue
Sales	31,700	60,600	82,200	106,400
Cubic Mission Solutions | Other
Disaggregation of Revenue
Sales	7,800	1,300	16,000	1,900
Cubic Global Defense Systems
Disaggregation of Revenue
Sales	84,400	74,700	165,900	151,800
Cubic Global Defense Systems | Fixed Price
Disaggregation of Revenue
Sales	75,600	68,200	149,900	139,800
Cubic Global Defense Systems | Other
Disaggregation of Revenue
Sales	$ 8,800	$ 6,500	$ 16,000	$ 12,000