Segment Information - Business Segment Financial Data (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Segment Information
Sales	$ 343,408	$ 321,482	$ 662,202	$ 650,321
Operating income (loss)	(25,555)	(29,934)	(24,258)	(36,417)
Depreciation and amortization	25,055	23,414	49,716	40,364
Cubic Transportation Systems
Segment Information
Sales	217,400	197,600	414,500	386,200
Operating income (loss)	33,000	12,600	64,700	26,900
Depreciation and amortization	7,500	7,400	15,000	14,500
Cubic Mission and Performance Solutions
Segment Information
Sales	126,000	123,900	247,700	264,100
Operating income (loss)	(22,300)	(25,700)	(38,800)	(34,300)
Depreciation and amortization	15,200	15,100	30,300	24,300
Corporate
Segment Information
Depreciation and amortization	2,300	900	4,400	1,600
Unallocated corporate expenses
Segment Information
Operating income (loss)	$ (36,300)	$ (16,800)	$ (50,200)	$ (29,000)