Variable Interest Entities - Net assets and liabilities (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
ASSETS
Other current assets					$ 43,705					$ 43,705		$ 43,705
Other noncurrent assets	$ 76,872								$ 76,872
Total assets	1,847,170				1,304,883				1,847,170	1,304,883	$ 1,336,300	1,321,130
LIABILITIES AND SHAREHOLDERS' EQUITY
Accrued compensation and other current liabilities					118,233					118,233		118,816
Long-term debt	189,111				199,793				189,111	199,793
Shareholders' equity related to Cubic	961,649				700,121				961,649	700,121		719,955
Noncontrolling interest in VIE	18,919				24,075				18,919	24,075		28,730
Total liabilities and shareholders' equity	1,847,170				1,304,883				1,847,170	1,304,883		$ 1,321,130
Revenue	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
Other income (expense), net									(19,957)	(687)	$ 364
VIE
ASSETS
Cash	347				374				347	374
Restricted cash	9,967				10,000				9,967	10,000
Other current assets	33								33
Long-term capitalized contract costs					33,818					33,818
Long-term contracts financing receivables	115,508								115,508
Other noncurrent assets	1,419				810				1,419	810
Total assets	127,274				45,002				127,274	45,002
LIABILITIES AND SHAREHOLDERS' EQUITY
Trade accounts payable	25				165				25	165
Accrued compensation and other current liabilities	191								191
Due to Cubic	25,143				11,724				25,143	11,724
Other long term liabilities	21,605				13				21,605	13
Long-term debt	61,994				9,056				61,994	9,056
Total liabilities	108,958				20,958				108,958	20,958
Shareholders' equity related to Cubic	(603)				(304)				(603)	(304)
Noncontrolling interest in VIE	18,919				24,348				18,919	24,348
Total liabilities and shareholders' equity	$ 127,274				$ 45,002				127,274	$ 45,002
Revenue									11,211
Operating income (loss)									9,923
Other income (expense), net									(21,592)
Interest income									3,704
Interest Expense									$ (2,946)