Segment Information - Sales by Geographical Region (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue
Total sales	$ 305,259	$ 248,391
Transportation Systems
Disaggregation of Revenue
Total sales	181,807	146,500
Cubic Mission Solutions
Disaggregation of Revenue
Total sales	46,393	33,100
Cubic Global Defense
Disaggregation of Revenue
Total sales	77,059	$ 68,800
United States
Disaggregation of Revenue
Total sales	172,500
United States | Transportation Systems
Disaggregation of Revenue
Total sales	91,300
United States | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	45,500
United States | Cubic Global Defense
Disaggregation of Revenue
Total sales	35,700
United Kingdom
Disaggregation of Revenue
Total sales	55,600
United Kingdom | Transportation Systems
Disaggregation of Revenue
Total sales	50,900
United Kingdom | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	400
United Kingdom | Cubic Global Defense
Disaggregation of Revenue
Total sales	4,300
Australia
Disaggregation of Revenue
Total sales	35,500
Australia | Transportation Systems
Disaggregation of Revenue
Total sales	29,800
Australia | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	100
Australia | Cubic Global Defense
Disaggregation of Revenue
Total sales	5,600
Far East/Middle East
Disaggregation of Revenue
Total sales	23,200
Far East/Middle East | Transportation Systems
Disaggregation of Revenue
Total sales	4,400
Far East/Middle East | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	400
Far East/Middle East | Cubic Global Defense
Disaggregation of Revenue
Total sales	18,400
Other foreign countries
Disaggregation of Revenue
Total sales	18,500
Other foreign countries | Transportation Systems
Disaggregation of Revenue
Total sales	5,400
Other foreign countries | Cubic Global Defense
Disaggregation of Revenue
Total sales	$ 13,100