Segment Information - Sales by End Customer (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
U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Total sales	252,300		613,600
Other
Disaggregation of Revenue
Total sales	130,400		411,700
Transportation Systems
Disaggregation of Revenue
Total sales	212,672	164,600	595,172	478,100
Transportation Systems | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Total sales	123,100		310,700
Transportation Systems | Other
Disaggregation of Revenue
Total sales	89,600		284,500
Cubic Mission Solutions
Disaggregation of Revenue
Total sales	94,978	42,700	203,306	111,900
Cubic Mission Solutions | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Total sales	91,800		195,600
Cubic Mission Solutions | Other
Disaggregation of Revenue
Total sales	3,200		7,700
Cubic Global Defense
Disaggregation of Revenue
Total sales	75,029	$ 88,900	226,799	$ 233,200
Cubic Global Defense | U.S. Federal Government and State and Local Municipalities
Disaggregation of Revenue
Total sales	37,400		107,300
Cubic Global Defense | Other
Disaggregation of Revenue
Total sales	$ 37,600		$ 119,500