Segment Information - Sales by Geographical Region (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
Transportation Systems
Disaggregation of Revenue
Total sales	212,672	164,600	595,172	478,100
Cubic Mission Solutions
Disaggregation of Revenue
Total sales	94,978	42,700	203,306	111,900
Cubic Global Defense
Disaggregation of Revenue
Total sales	75,029	$ 88,900	226,799	$ 233,200
United States
Disaggregation of Revenue
Total sales	254,500		628,700
United States | Transportation Systems
Disaggregation of Revenue
Total sales	128,900		327,300
United States | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	94,000		200,100
United States | Cubic Global Defense
Disaggregation of Revenue
Total sales	31,600		101,300
United Kingdom
Disaggregation of Revenue
Total sales	55,400		169,200
United Kingdom | Transportation Systems
Disaggregation of Revenue
Total sales	47,500		151,600
United Kingdom | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	200		1,300
United Kingdom | Cubic Global Defense
Disaggregation of Revenue
Total sales	7,700		16,300
Australia
Disaggregation of Revenue
Total sales	39,300		112,300
Australia | Transportation Systems
Disaggregation of Revenue
Total sales	30,900		91,100
Australia | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	300		500
Australia | Cubic Global Defense
Disaggregation of Revenue
Total sales	8,100		20,700
Far East/Middle East
Disaggregation of Revenue
Total sales	16,000		55,000
Far East/Middle East | Transportation Systems
Disaggregation of Revenue
Total sales	700		8,500
Far East/Middle East | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	100		700
Far East/Middle East | Cubic Global Defense
Disaggregation of Revenue
Total sales	15,200		45,800
Other foreign countries
Disaggregation of Revenue
Total sales	17,500		60,100
Other foreign countries | Transportation Systems
Disaggregation of Revenue
Total sales	4,700		16,700
Other foreign countries | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	400		700
Other foreign countries | Cubic Global Defense
Disaggregation of Revenue
Total sales	$ 12,400		$ 42,700