Segment Information - Sales by Geographical Region (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
Transportation Systems
Disaggregation of Revenue
Total sales	200,693	167,000	382,500	313,500
Cubic Mission Solutions
Disaggregation of Revenue
Total sales	61,935	36,100	108,328	69,200
Cubic Global Defense
Disaggregation of Revenue
Total sales	74,711	$ 75,500	151,770	$ 144,300
United States
Disaggregation of Revenue
Total sales	201,400		373,900
United States | Transportation Systems
Disaggregation of Revenue
Total sales	106,900		198,200
United States | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	60,500		106,000
United States | Cubic Global Defense
Disaggregation of Revenue
Total sales	34,000		69,700
United Kingdom
Disaggregation of Revenue
Total sales	58,200		113,800
United Kingdom | Transportation Systems
Disaggregation of Revenue
Total sales	53,200		104,100
United Kingdom | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	700		1,100
United Kingdom | Cubic Global Defense
Disaggregation of Revenue
Total sales	4,300		8,600
Australia
Disaggregation of Revenue
Total sales	37,600		73,100
Australia | Transportation Systems
Disaggregation of Revenue
Total sales	30,400		60,200
Australia | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	100		200
Australia | Cubic Global Defense
Disaggregation of Revenue
Total sales	7,100		12,700
Far East/Middle East
Disaggregation of Revenue
Total sales	16,000		39,200
Far East/Middle East | Transportation Systems
Disaggregation of Revenue
Total sales	3,500		7,900
Far East/Middle East | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	200		600
Far East/Middle East | Cubic Global Defense
Disaggregation of Revenue
Total sales	12,300		30,700
Other foreign countries
Disaggregation of Revenue
Total sales	24,100		42,600
Other foreign countries | Transportation Systems
Disaggregation of Revenue
Total sales	6,700		12,100
Other foreign countries | Cubic Mission Solutions
Disaggregation of Revenue
Total sales	400		400
Other foreign countries | Cubic Global Defense
Disaggregation of Revenue
Total sales	$ 17,000		$ 30,100