Acquisitions and Divestitures - Goodwill and Pro forma information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Unaudited pro forma information
Net sales	$ 350,400	$ 384,400	$ 1,005,000	$ 1,050,200
Net loss attributable to Cubic	(1,400)	$ 14,400	(69,500)	$ (18,800)
Adjustments made for transaction expenses			0
Changes in the carrying amount of goodwill
Net balances at the beginning of the period			578,097
Acquisitions			204,152
Adjustments			603
Foreign currency exchange rate changes			516
Net balance at the end of the period	783,368		783,368
Cubic Transportation Systems
Changes in the carrying amount of goodwill
Net balances at the beginning of the period			254,592
Acquisitions			30,621
Adjustments			603
Foreign currency exchange rate changes			329
Net balance at the end of the period	286,145		286,145
Cubic Mission Solutions
Changes in the carrying amount of goodwill
Net balances at the beginning of the period			181,424
Acquisitions			173,531
Foreign currency exchange rate changes			85
Net balance at the end of the period	355,040		355,040
Cubic Global Defense Systems
Changes in the carrying amount of goodwill
Net balances at the beginning of the period			142,081
Foreign currency exchange rate changes			102
Net balance at the end of the period	$ 142,183		$ 142,183