Business Segment Information - Financial data (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Information
Sales	$ 379,709	$ 296,212	$ 278,586	$ 248,391	$ 349,115	$ 266,184	$ 248,040	$ 244,370	$ 1,202,898	$ 1,107,709	$ 1,070,601
Operating income (loss)	27,673	$ 10,290	$ (1,679)	$ (11,902)	21,207	$ (6,872)	$ (6,084)	$ (5,623)	24,382	2,628	(11,649)
Assets	1,304,883				1,336,285				1,304,883	1,336,285	1,504,700
Assets - Discontinued Operations					174,200					174,200	185,500
Depreciation and amortization									46,600	48,045	40,323
Capital expenditures									31,696	36,916	32,093
Transportation Systems
Segment Information
Sales									670,700	578,600	586,400
Operating income (loss)									60,400	39,800	57,500
Assets	390,200				335,100				390,200	335,100	338,200
Depreciation and amortization									12,000	8,800	8,200
Capital expenditures									3,200	6,900	2,200
Cubic Global Defense
Segment Information
Sales									325,200	360,200	374,700
Operating income (loss)									16,600	28,100	19,900
Assets	360,100				280,100				360,100	280,100	211,800
Depreciation and amortization									8,500	10,400	7,500
Capital expenditures									9,400	5,900	6,800
Cubic Mission Solutions
Segment Information
Sales									207,000	168,900	109,500
Operating income (loss)									(100)	(9,300)	(37,000)
Assets	352,900				390,500				352,900	390,500	404,400
Depreciation and amortization									22,400	23,800	21,200
Capital expenditures									2,100	1,700	2,100
Corporate
Segment Information
Assets	$ 201,700				$ 156,400				201,700	156,400	364,800
Depreciation and amortization									3,700	5,000	3,400
Capital expenditures									17,000	22,400	21,000
Unallocated corporate expenses and other
Segment Information
Operating income (loss)									$ (52,500)	$ (56,000)	$ (52,000)