Segment Information - Business Segment Financial Data (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Information
Sales	$ 318,794	$ 328,839
Operating income (loss)	1,297	(6,483)
Depreciation and amortization	24,661	16,950
Cubic Transportation Systems
Segment Information
Sales	197,100	188,600
Operating income (loss)	31,700	14,300
Depreciation and amortization	7,500	7,100
Cubic Mission and Performance Solutions
Segment Information
Sales	121,700	140,200
Operating income (loss)	(16,500)	(8,600)
Depreciation and amortization	15,100	9,200
Corporate
Segment Information
Depreciation and amortization	2,100	700
Unallocated corporate expenses
Segment Information
Operating income (loss)	$ (13,900)	$ (12,200)