Segment Information - Business Segment Financial Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Information
Sales	$ 350,439	$ 382,679	$ 1,000,760	$ 1,025,277
Operating income (loss)	24,706	34,725	(11,711)	27,618
Depreciation and amortization	23,394	15,351	63,758	48,949
Cubic Transportation Systems
Segment Information
Sales	215,500	212,700	601,800	595,200
Operating income (loss)	50,900	17,200	77,800	37,000
Depreciation and amortization	7,100	6,900	21,600	24,100
Cubic Mission Solutions
Segment Information
Sales	69,000	95,000	167,200	203,300
Operating income (loss)	(21,300)	1,300	(67,600)	(12,100)
Depreciation and amortization	13,300	6,000	34,300	17,200
Cubic Global Defense Systems
Segment Information
Sales	65,900	75,000	231,800	226,800
Operating income (loss)	6,100	1,900	18,100	10,000
Depreciation and amortization	1,900	1,700	5,200	5,400
Corporate
Segment Information
Depreciation and amortization	1,100	700	2,700	2,200
Unallocated corporate expenses
Segment Information
Operating income (loss)	$ (11,000)	$ 14,300	$ (40,000)	$ (7,300)