Fair Value of Financial Instruments - Contingent Consideration (Details) $ in Thousands, item in Millions		3 Months Ended	12 Months Ended
	Jan. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) item	Sep. 30, 2020 USD ($)	Jan. 03, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Assets and liabilities measured at fair value on a recurring basis
Assets		$ 2,299,598	$ 2,324,221
Franklin Blackhorse, L.P
Assets and liabilities measured at fair value on a recurring basis
Investment			1,200		$ 5,000
Franklin Blackhorse, L.P | Other Assets
Assets and liabilities measured at fair value on a recurring basis
Assets		5,500	5,600
Franklin Blackhorse, L.P | Other income (expense)
Assets and liabilities measured at fair value on a recurring basis
Net loss from equity method investment		(100)
Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		10,618
Total remeasurement (gain) loss recognized in earnings		(576)
Balance at the ending period		10,042	10,618
H4 Global | Subsequent event
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration for certain goals	$ 1,300
H4 Global | Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		1,148
Total remeasurement (gain) loss recognized in earnings		148
Balance at the ending period		1,296	1,148
Deltenna | Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		3,004
Total remeasurement (gain) loss recognized in earnings		176
Balance at the ending period		3,180	$ 3,004
Deltenna | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration for certain goals		$ 7,400
Deltenna | Volatility for underlying revenue metrics
Assets and liabilities measured at fair value on a recurring basis
Measurement inputs for contingent consideration		52
Deltenna | Discount Rate
Assets and liabilities measured at fair value on a recurring basis
Measurement inputs for contingent consideration		10.5	10.5
Shield Aviation
Assets and liabilities measured at fair value on a recurring basis
Determination of fair value of contingent consideration | item		1
Revenue risk adjustment used in determination of fair value of contingent consideration			16.00%
Shield Aviation | Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		$ 5,566
Balance at the ending period		5,566	$ 5,566
Shield Aviation | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration for certain goals		$ 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		31.00%
Shield Aviation | Discount Rate
Assets and liabilities measured at fair value on a recurring basis
Measurement inputs for contingent consideration		5.7	5.7
Nuvotronics
Assets and liabilities measured at fair value on a recurring basis
Determination of fair value of contingent consideration | item		1
Period for contingent consideration contracts		12 months
Contingent consideration, fair value		$ 0
Nuvotronics | Maximum
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration for certain goals		8,000
Delerrok Inc.
Assets and liabilities measured at fair value on a recurring basis
Contingent consideration				$ 1,600
Investment					$ 8,300	$ 8,300
Contingent consideration, fair value		0
Delerrok Inc. | Level 3
Change in fair value of our Level 3 contingent consideration
Balance at the Beginning period		900
Total remeasurement (gain) loss recognized in earnings		$ (900)
Balance at the ending period			$ 900