Fair Value of Financial Instruments - Contingent Consideration (Details) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2018 USD ($) item	Dec. 31, 2018 USD ($) item	Sep. 30, 2018 USD ($) item
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 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		9,114
Cash paid to seller		(1,750)
Total remeasurement (gain) loss recognized in earnings		429
Balance at the ending period		7,793	$ 9,114
Deltenna | Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		1,081
Total remeasurement (gain) loss recognized in earnings		262
Balance at the ending period		1,343	$ 1,081
Deltenna | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		$ 6,900
Deltenna | Volatility for underlying revenue metrics
Assets and liabilities measured at fair value on a recurring basis
Measurement inputs for contingent consideration | item		40	53
Shield Aviation
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration	$ 5,600
Iterations used in determination of fair value of contingent consideration | item	100,000
Revenue risk adjustment used in determination of fair value of contingent consideration			0.14%
Shield Aviation | Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		$ 5,618
Balance at the ending period		5,618	$ 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
Measurement inputs for contingent consideration			0.20
Shield Aviation | Discount Rate
Assets and liabilities measured at fair value on a recurring basis
Measurement inputs for contingent consideration		0.050	0.050
TeraLogics | Level 3 | Revenue Targets
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		$ 1,750
Cash paid to seller		$ (1,750)
Balance at the ending period			$ 1,750
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
Total remeasurement (gain) loss recognized in earnings		167
Balance at the ending period		832	$ 665
H4 Global | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		$ 3,200