Implementation of the New Revenue Recognition Standard - Impact on segment net sales and operating income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	$ 382,679	$ 296,212	$ 1,025,277	$ 823,189
Operating income (loss)	34,725	10,290	27,618	(3,291)
ASU 2014-09 | ASC 605
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	367,394		953,853
Operating income (loss)	31,087		15,256
ASU 2014-09 | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	15,285		71,424
Operating income (loss)	3,638		12,362
Unallocated corporate expenses and other
Revenue, Initial Application Period Cumulative Effect Transition
Operating income (loss)	14,290	(14,700)	(7,295)	(42,400)
Unallocated corporate expenses and other | ASU 2014-09 | ASC 605
Revenue, Initial Application Period Cumulative Effect Transition
Operating income (loss)	14,290		(7,295)
Transportation Systems
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	212,672	164,600	595,172	478,100
Operating income (loss)	17,277	18,600	37,048	42,700
Transportation Systems | ASU 2014-09 | ASC 605
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	201,935		557,234
Operating income (loss)	14,489		29,348
Transportation Systems | ASU 2014-09 | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	10,737		37,938
Operating income (loss)	2,788		7,700
Cubic Mission Solutions
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	94,978	42,700	203,306	111,900
Operating income (loss)	1,230	(500)	(12,133)	(17,200)
Cubic Mission Solutions | ASU 2014-09 | ASC 605
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	94,352		202,392
Operating income (loss)	1,187		(12,045)
Cubic Mission Solutions | ASU 2014-09 | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	626		914
Operating income (loss)	43		(88)
Cubic Global Defense
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	75,029	88,900	226,799	233,200
Operating income (loss)	1,928	$ 6,900	9,998	$ 13,600
Cubic Global Defense | ASU 2014-09 | ASC 605
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	71,107		194,227
Operating income (loss)	1,121		5,248
Cubic Global Defense | ASU 2014-09 | ASC 606
Revenue, Initial Application Period Cumulative Effect Transition
Net sales	3,922		32,572
Operating income (loss)	$ 807		$ 4,750