Goodwill and Purchased Intangible Assets - Intangible assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Purchased intangible assets
Gross Carrying Amount	$ 275,795	$ 266,974
Accumulated Amortization	(177,300)	(143,571)
Net Carrying Amount	98,495	123,403
Amortization expense	32,997	34,120	$ 27,550
Expected amortization for purchased intangibles for each of the next five years
2018	28,028
2019	21,611
2020	15,266
2021	11,480
2022	8,217
Thereafter	13,893
Total expected amortization for purchased intangibles	98,495
Contract and program intangibles
Purchased intangible assets
Gross Carrying Amount	214,215	209,511
Accumulated Amortization	(151,422)	(123,645)
Net Carrying Amount	62,793	85,866
Other purchased intangibles
Purchased intangible assets
Gross Carrying Amount	61,580	57,463
Accumulated Amortization	(25,878)	(19,926)
Net Carrying Amount	35,702	$ 37,537
Transportation Systems
Expected amortization for purchased intangibles for each of the next five years
2018	4,944
2019	2,886
2020	947
2021	698
2022	598
Thereafter	297
Total expected amortization for purchased intangibles	10,370
Defense Systems
Expected amortization for purchased intangibles for each of the next five years
2018	21,009
2019	17,291
2020	13,529
2021	10,075
2022	6,912
Thereafter	10,673
Total expected amortization for purchased intangibles	79,489
Cubic Global Defense Services
Expected amortization for purchased intangibles for each of the next five years
2018	2,075
2019	1,434
2020	790
2021	707
2022	707
Thereafter	2,923
Total expected amortization for purchased intangibles	$ 8,636