Summary of Significant Accounting Polices - ASC 606 (Details) - USD ($) $ / shares in Units, $ 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
Revenue, Initial Application Period Cumulative Effect Transition
Equity	$ 980,568				$ 724,196				$ 980,568	$ 724,196		$ 748,685
Operating income (loss)	$ 58,619	$ 34,725	$ (6,541)	$ (566)	$ 27,673	$ 10,290	$ (1,679)	$ (11,902)	86,237	24,382	$ 2,628
Net income (loss) from continuing operations									$ 41,306	$ 7,793	$ (25,740)
Diluted earnings per share attributable to Cubic (in dollars per share)	$ 1.38	$ 0.77	$ (0.30)	$ (0.23)	$ 0.65	$ 0.23	$ (0.07)	$ (0.36)	$ 1.62	$ 0.45	$ (0.41)
ASU 2014-09 | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition
Equity	$ 45,519				$ 24,489				$ 45,519	$ 24,489
Operating income (loss)									14,885
Net income (loss) from continuing operations									$ 21,029
Diluted earnings per share attributable to Cubic (in dollars per share)									$ 0.29
ASU 2014-09 | ASC 606 | Change in Estimates
Revenue, Initial Application Period Cumulative Effect Transition
Operating income (loss)	(1,420)				(4,162)				$ (2,235)	(6,986)	$ 5,737
Net income (loss) from continuing operations	$ (1,615)				$ (3,149)				$ (2,351)	$ (5,146)	$ 3,208
Diluted earnings per share attributable to Cubic (in dollars per share)	$ (0.05)				$ (0.12)				$ (0.08)	$ (0.19)	$ 0.12
ASU 2014-09 | Adjustments
Revenue, Initial Application Period Cumulative Effect Transition
Equity												$ 24,500