Summary of Quarterly Results of Operations (Unaudited)) - Impact (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition
Operating income (loss)	$ 73,286	$ 24,706	$ (29,934)	$ (6,483)	$ 58,619	$ 34,725	$ (6,541)	$ (566)	$ 61,575	$ 86,237	$ 24,382
Net income (loss) from continuing operations attributable to Cubic									$ 2,935	$ 41,306	$ 7,793
Diluted earnings (loss) per share attributable to Cubic (in dollars per share)	$ 1.84	$ (0.04)	$ (1.25)	$ (0.66)	$ 1.38	$ 0.77	$ (0.30)	$ (0.23)	$ (0.10)	$ 1.62	$ 0.45
ASU 2014-09 | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition
Operating income (loss)									$ 7,527	$ (2,235)	$ (6,986)
Diluted earnings (loss) per share attributable to Cubic (in dollars per share)									$ (0.26)	$ (0.08)	$ (0.19)
ASU 2014-09 | ASC 606 | Change in Estimates
Revenue, Initial Application Period Cumulative Effect Transition
Operating income (loss)	$ 3,173				$ (1,420)
Net income (loss) from continuing operations attributable to Cubic	$ 1,946				$ (1,615)
Diluted earnings (loss) per share attributable to Cubic (in dollars per share)	$ 0.06				$ (0.05)