Variable Interest Entities - Net assets and liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
ASSETS
Other noncurrent assets	$ 25,424		$ 25,424		$ 21,759
Total assets	2,401,458		2,401,458		2,324,221
LIABILITIES AND SHAREHOLDERS' EQUITY
Total Cubic equity	927,754		927,754		960,777
Total liabilities and shareholders' equity	2,401,458		2,401,458		2,324,221
Revenue	343,408	$ 321,482	662,202	$ 650,321
Operating income	(25,555)	(29,934)	(24,258)	(36,417)
Other income (expense), net	14,543	(19,664)	15,839	(19,791)
VIE
ASSETS
Cash	1,546		1,546		1,065
Restricted cash	7,322		7,322		1,822
Other current assets	18		18		31
Long-term contracts financing receivables	257,185		257,185		221,245
Other noncurrent assets	12,454		12,454
Total assets	278,525		278,525		224,163
LIABILITIES AND SHAREHOLDERS' EQUITY
Trade accounts payable	35		35		49
Accrued compensation and other current liabilities	109		109		85
Due to Cubic	17,262		17,262		27,259
Other noncurrent liabilities					5,890
Long-term debt	208,594		208,594		163,348
Total liabilities	226,000		226,000		196,631
Total Cubic equity	2,628		2,628		129
Noncontrolling interests	49,897		49,897		27,403
Total liabilities and shareholders' equity	278,525		278,525		$ 224,163
Revenue	4,616	1,802	8,637	3,047
Operating income	4,184	1,516	7,901	2,488
Other income (expense), net	15,091	(15,819)	18,343	(12,748)
Interest income	1,487	1,655	2,860	3,208
Interest Expense	$ (2,122)	$ (1,995)	$ (4,111)	$ (3,154)