Fair Value of Financial Instruments - Contingent Consideration (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 USD ($)	Mar. 31, 2019 USD ($)	Jul. 31, 2018 USD ($)
Franklin Blackhorse, L.P
Assets and liabilities measured at fair value on a recurring basis
Investment	$ 5,000
Franklin Blackhorse, L.P | Other Assets
Assets and liabilities measured at fair value on a recurring basis
Investment	5,300
Franklin Blackhorse, L.P | Other income (expense)
Assets and liabilities measured at fair value on a recurring basis
Income (Loss) from Equity Method Investments	300
Cubic Global Defense Services | Disposed of by sale
Assets and liabilities measured at fair value on a recurring basis
Receivable for estimated earn-out amount due from purchaser	3,000
Level 2
Debt instruments
Fair Value	203,300	$ 193,700
Carrying value	200,000	200,000
Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period	9,114	5,217
Initial measurement recognized at acquisition	4,900	5,618
Cash paid to seller	(2,135)	(2,750)
Total remeasurement (gain) loss recognized in earnings	(1,005)	1,029
Balance at the ending period	10,874	9,114
Deltenna | Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period	1,081	1,376
Total remeasurement (gain) loss recognized in earnings	706	(295)
Balance at the ending period	1,787	$ 1,081
Deltenna | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration	$ 6,600
Deltenna | Volatility for underlying revenue metrics
Assets and liabilities measured at fair value on a recurring basis
Measurement inputs for contingent consideration	36	53
Deltenna | Discount Rate
Assets and liabilities measured at fair value on a recurring basis
Measurement inputs for contingent consideration	11	11.5
Shield Aviation
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration				$ 5,600
Determination of fair value of contingent consideration | item	1,000,000
Revenue risk adjustment used in determination of fair value of contingent consideration	13.10%	14.50%
Shield Aviation | Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period	$ 5,618
Initial measurement recognized at acquisition		$ 5,618
Total remeasurement (gain) loss recognized in earnings	(1,804)
Balance at the ending period	3,814	$ 5,618
Shield Aviation | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration	$ 10,000			$ 10,000
Shield Aviation | Volatility for underlying revenue metrics
Assets and liabilities measured at fair value on a recurring basis
Volatility for underlying earnings metrics used in determination of fair value of contingent consideration	18.00%	20.00%
Shield Aviation | Discount Rate
Assets and liabilities measured at fair value on a recurring basis
Measurement inputs for contingent consideration	3.6	3.9
TeraLogics | Level 3 | Revenue Targets
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period	$ 1,750	$ 2,450
Cash paid to seller	$ (1,750)	(1,750)
Total remeasurement (gain) loss recognized in earnings		1,050
Balance at the ending period		1,750
TeraLogics | Level 3 | Contract extensions
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		800
Cash paid to seller		(1,000)
Total remeasurement (gain) loss recognized in earnings		200
H4 Global
Assets and liabilities measured at fair value on a recurring basis
Period for contingent consideration contracts	5 years
H4 Global | Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period	$ 665	591
Cash paid to seller	(385)
Total remeasurement (gain) loss recognized in earnings	793	74
Balance at the ending period	1,073	$ 665
H4 Global | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration	$ 2,700
Nuvotronics
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration			$ 4,900
Determination of fair value of contingent consideration | item	1,000,000
Period for contingent consideration contracts	12 months
Nuvotronics | Level 3
Change in fair value of our Level 3 contingent consideration
Initial measurement recognized at acquisition	$ 4,900
Total remeasurement (gain) loss recognized in earnings	(700)
Balance at the ending period	4,200
Nuvotronics | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration	$ 8,000		$ 8,000
Nuvotronics | Volatility for underlying revenue metrics
Assets and liabilities measured at fair value on a recurring basis
Volatility for underlying earnings metrics used in determination of fair value of contingent consideration	12.40%
Nuvotronics | Discount Rate
Assets and liabilities measured at fair value on a recurring basis
Measurement inputs for contingent consideration	7.4