Segment Information - Business segment financial data (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Revenue recognition
Sales	$ 278,586	$ 248,040	$ 526,977	$ 492,410
Operating loss	(1,679)	(6,084)	(13,581)	(11,707)
Depreciation and amortization	11,058	11,611	23,491	24,036
Transportation Systems
Revenue recognition
Sales	167,000	139,600	313,500	271,500
Operating loss	14,200	7,800	24,100	17,500
Depreciation and amortization	3,000	2,000	6,200	4,400
Defense Systems
Revenue recognition
Sales	75,500	79,700	144,300	158,300
Operating loss	5,300	4,800	6,700	8,100
Depreciation and amortization	1,500	1,800	3,200	3,800
Cubic Mission Solutions
Revenue recognition
Sales	36,100	28,700	69,200	62,600
Operating loss	(7,800)	(9,200)	(16,700)	(13,000)
Depreciation and amortization	5,200	5,900	11,100	12,700
Corporate
Revenue recognition
Depreciation and amortization	1,400	1,900	3,000	3,100
Unallocated corporate expenses and other
Revenue recognition
Operating loss	$ (13,400)	$ (9,500)	$ (27,700)	$ (24,300)