Segment Information - Sales by Contract Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue
Total sales	$ 337,339	$ 278,586	$ 642,598	$ 526,977
Fixed Price
Disaggregation of Revenue
Total sales	326,300		621,900
Other
Disaggregation of Revenue
Total sales	11,000		20,700
Transportation Systems
Disaggregation of Revenue
Total sales	200,693	167,000	382,500	313,500
Transportation Systems | Fixed Price
Disaggregation of Revenue
Total sales	197,500		375,700
Transportation Systems | Other
Disaggregation of Revenue
Total sales	3,200		6,800
Cubic Mission Solutions
Disaggregation of Revenue
Total sales	61,935	36,100	108,328	69,200
Cubic Mission Solutions | Fixed Price
Disaggregation of Revenue
Total sales	60,600		106,400
Cubic Mission Solutions | Other
Disaggregation of Revenue
Total sales	1,300		1,900
Cubic Global Defense
Disaggregation of Revenue
Total sales	74,711	$ 75,500	151,770	$ 144,300
Cubic Global Defense | Fixed Price
Disaggregation of Revenue
Total sales	68,200		139,800
Cubic Global Defense | Other
Disaggregation of Revenue
Total sales	$ 6,500		$ 12,000