Business Segment Information - Financial data (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2017 USD ($) segment	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Revenue recognition
Number of primary business segments | segment									3
Sales	$ 445,606	$ 361,869	$ 343,709	$ 334,677	$ 406,588	$ 375,240	$ 366,024	$ 313,813	$ 1,485,861	$ 1,461,665	$ 1,431,045
Operating income (Loss)	25,384	$ (1,697)	$ (2,072)	$ (4,101)	10,488	$ 13,893	$ (9,086)	$ (8,077)	17,514	7,218	75,387
Assets	1,336,285				1,504,408				1,336,285	1,504,408	1,300,300
Depreciation and amortization									51,099	45,478	37,662
Capital expenditures									36,932	32,093	22,202
Transportation Systems
Revenue recognition
Sales									578,600	586,400	566,800
Operating income (Loss)									39,800	57,500	75,900
Assets	335,100				338,200				335,100	338,200	410,000
Depreciation and amortization									8,800	8,200	10,800
Capital expenditures									6,900	2,200	2,000
Defense Systems
Revenue recognition
Sales									529,100	484,200	462,100
Operating income (Loss)									18,800	(17,100)	18,400
Assets	670,600				616,200				670,600	616,200	341,200
Depreciation and amortization									32,900	28,700	17,100
Capital expenditures									7,600	8,900	600
Cubic Global Defense Services
Revenue recognition
Sales									378,200	391,100	402,100
Operating income (Loss)									6,700	11,200	6,600
Assets	179,400				191,200				179,400	191,200	200,700
Depreciation and amortization									3,100	5,200	8,500
Corporate and other
Revenue recognition
Assets	$ 151,200				$ 359,100				151,200	359,100	348,400
Depreciation and amortization									6,300	3,400	1,300
Capital expenditures									22,400	21,000	19,600
Unallocated corporate expenses and other
Revenue recognition
Operating income (Loss)									$ (47,800)	$ (44,400)	$ (25,500)