Implementation of the New Revenue Recognition Standard - Impact on segment net sales and operating income (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
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	$ 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
ASU 2014-09 | ASC 605
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									1,387,276
Operating income (loss)									71,352
ASU 2014-09 | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									109,199
Operating income (loss)									14,885
Unallocated corporate expenses and other
Revenue, Initial Application Period Cumulative Effect Transition
Operating income (loss)									(21,724)	(52,500)	(56,000)
Unallocated corporate expenses and other | ASU 2014-09 | ASC 605
Revenue, Initial Application Period Cumulative Effect Transition
Operating income (loss)									(21,724)
Cubic Transportation Systems
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									849,779	670,700	578,600
Operating income (loss)									77,233	60,400	39,800
Cubic Transportation Systems | ASU 2014-09 | ASC 605
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									787,936
Operating income (loss)									65,974
Cubic Transportation Systems | ASU 2014-09 | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									61,843
Operating income (loss)									11,259
Cubic Mission Solutions
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									328,771	207,000	168,900
Operating income (loss)									7,759	(100)	(9,300)
Cubic Mission Solutions | ASU 2014-09 | ASC 605
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									327,139
Operating income (loss)									7,244
Cubic Mission Solutions | ASU 2014-09 | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									1,632
Operating income (loss)									515
Cubic Global Defense
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									317,925	325,200	360,200
Operating income (loss)									22,969	$ 16,600	$ 28,100
Cubic Global Defense | ASU 2014-09 | ASC 605
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									272,201
Operating income (loss)									19,858
Cubic Global Defense | ASU 2014-09 | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition
Net sales									45,724
Operating income (loss)									$ 3,111