Segment Information - Sales by Contract Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue
Total sales	$ 382,679	$ 296,212	$ 1,025,277	$ 823,189
Fixed Price
Disaggregation of Revenue
Total sales	373,200		995,300
Other
Disaggregation of Revenue
Total sales	9,500		30,000
Transportation Systems
Disaggregation of Revenue
Total sales	212,672	164,600	595,172	478,100
Transportation Systems | Fixed Price
Disaggregation of Revenue
Total sales	210,500		586,300
Transportation Systems | Other
Disaggregation of Revenue
Total sales	2,200		8,900
Cubic Mission Solutions
Disaggregation of Revenue
Total sales	94,978	42,700	203,306	111,900
Cubic Mission Solutions | Fixed Price
Disaggregation of Revenue
Total sales	93,200		199,600
Cubic Mission Solutions | Other
Disaggregation of Revenue
Total sales	1,800		3,700
Cubic Global Defense
Disaggregation of Revenue
Total sales	75,029	$ 88,900	226,799	$ 233,200
Cubic Global Defense | Fixed Price
Disaggregation of Revenue
Total sales	69,500		209,400
Cubic Global Defense | Other
Disaggregation of Revenue
Total sales	$ 5,500		$ 17,400