Fair Value of Financial Instruments - Contingent Consideration (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
	Oct. 01, 2015	Jun. 30, 2018	Sep. 30, 2017	Jul. 31, 2017
Cubic Global Defense Services | Discontinued operations held-for-sale
Assets and liabilities measured at fair value on a recurring basis
Additional cash payment to be received based on achievement of pre-determined earn-out conditions		$ 3,000
Deltenna
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration				$ 1,300
Volatility earning metrics		45.00%	40.00%
Deltenna | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		$ 7,100		$ 7,600
TeraLogics
Assets and liabilities measured at fair value on a recurring basis
Volatility earning metrics		20.00%	15.00%
H4 Global
Assets and liabilities measured at fair value on a recurring basis
Period for contingent consideration contracts	5 years
H4 Global | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		$ 3,300
Revenue Targets | TeraLogics | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		1,800
Contract extensions | TeraLogics | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration		1,000
Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		5,217
Cash paid to seller		(1,750)
Total remeasurement (gain) loss recognized in earnings		446
Balance at the ending period		3,913	$ 5,217
Level 3 | Deltenna
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		1,376
Total remeasurement (gain) loss recognized in earnings		(280)
Balance at the ending period		1,096	1,376
Level 3 | H4 Global
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		591
Total remeasurement (gain) loss recognized in earnings		176
Balance at the ending period		767	591
Level 3 | Revenue Targets | TeraLogics
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		2,450
Cash paid to seller		(1,750)
Total remeasurement (gain) loss recognized in earnings		400
Balance at the ending period		1,100	2,450
Level 3 | Contract extensions | TeraLogics
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		800
Total remeasurement (gain) loss recognized in earnings		150
Balance at the ending period		$ 950	$ 800