Business Segment Information - Financial data (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Oct. 01, 2018
Segment Information
Sales	$ 471,198	$ 382,679	$ 337,339	$ 305,259	$ 379,709	$ 296,212	$ 278,586	$ 248,391	$ 1,496,475	$ 1,202,898	$ 1,107,709
Operating income (loss)	58,619	$ 34,725	$ (6,541)	$ (566)	27,673	$ 10,290	$ (1,679)	$ (11,902)	86,237	24,382	2,628
Assets	1,847,170				1,304,883				1,847,170	1,304,883	1,336,300	$ 1,321,130
Assets - Discontinued Operations											174,200
Depreciation and amortization									64,742	46,600	48,045
Capital expenditures									49,084	31,696	36,916
Cubic Transportation Systems
Segment Information
Sales									849,779	670,700	578,600
Operating income (loss)									77,233	60,400	39,800
Assets	825,800				390,200				825,800	390,200	335,100
Depreciation and amortization									30,700	12,000	8,800
Capital expenditures									6,600	3,200	6,900
Cubic Mission Solutions
Segment Information
Sales									328,771	207,000	168,900
Operating income (loss)									7,759	(100)	(9,300)
Assets	437,900				352,900				437,900	352,900	390,500
Depreciation and amortization									23,300	22,400	23,800
Capital expenditures									11,100	2,100	1,700
Cubic Global Defense
Segment Information
Sales									317,925	325,200	360,200
Operating income (loss)									22,969	16,600	28,100
Assets	394,200				360,100				394,200	360,100	280,100
Depreciation and amortization									6,800	8,500	10,400
Capital expenditures									4,500	9,400	5,900
Corporate
Segment Information
Assets	$ 189,300				$ 201,700				189,300	201,700	156,400
Depreciation and amortization									3,900	3,700	5,000
Capital expenditures									26,900	17,000	22,400
Unallocated corporate expenses and other
Segment Information
Operating income (loss)									$ (21,724)	$ (52,500)	$ (56,000)