Acquisitions, Dispositions, and Deconsolidations - Spectrum Segment, Insurance Segment and Other Segments Narrative (Details) $ in Thousands								3 Months Ended						9 Months Ended
	Jul. 01, 2021 USD ($)	Jan. 15, 2021 USD ($)	Oct. 31, 2020 USD ($)	May 12, 2020 USD ($)	Feb. 28, 2020 USD ($)	Jan. 30, 2020 USD ($)	Oct. 30, 2019 USD ($) tranche	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Cash received from dispositions, net of cash disposed														$ 74,000	$ 144,000
Gain (loss) on sale of subsidiary														(159,900)	(39,300)
Loss on disposal of subsidiary								$ 334,000			$ 0			334,000	(22,100)
Foreign currency translation adjustment								1,200			500			2,400	(3,500)
Accumulated other comprehensive income								3,200		$ 396,900				3,200
Cash and cash equivalents								55,500		43,800	28,200			55,500	28,200	$ 23,300
Investments								49,900		55,400				$ 49,900
Discontinued Operations
Business Acquisition [Line Items]
Gain (loss) on sale of subsidiary								$ (200,300)			$ 0				$ (39,300)
CIG | Discontinued Operations
Business Acquisition [Line Items]
Gain (loss) on sale of subsidiary	$ (200,800)
Beneficial ownership interest								6.60%						6.60%
CIG | Discontinued Operations | Insurance
Business Acquisition [Line Items]
Segment book value	544,000
Accumulated other comprehensive income	344,000
Cash and cash equivalents	62,500
Investments	$ 26,700
GMSL
Business Acquisition [Line Items]
Ownership percentage before sale of stock						100.00%
Consideration to be received						$ 250,000	$ 140,000
Potential earn-out, maximum						$ 12,500
Proceeds from divestiture of businesses					$ 144,000							$ 85,500
Cash received from dispositions, net of cash disposed					100,800
Consideration held in escrow for future losses payable					1,250
Consideration held of escrow for purchase price adjustment					1,910
Consideration paid on the earlier of December 31, 2020 or the date on which a cash collateralized bond in connection with Company's bonding facility is released					2,400
Gain (loss) on sale of subsidiary									$ 1,200	2,400			$ (39,300)
Loss on disposal of subsidiary													$ 31,300
Realized gain on disposal				$ 71,100
Tax expense				7,200
GMSL | Discontinued Operations
Business Acquisition [Line Items]
Gain (loss) on sale of subsidiary					(39,300)				$ 1,200	$ 2,400
Loss on disposal of subsidiary					31,300
GMSL | Put option
Business Acquisition [Line Items]
Realized gain on disposal				$ 11,300
GMSL | Non- controlling Interest
Business Acquisition [Line Items]
Proceeds from divestiture of businesses												17,500
Cash divested from deconsolidation					36,800
GMSL | Noncontrolling Interest Redeemable
Business Acquisition [Line Items]
Proceeds from divestiture of businesses												$ 2,100
Cash divested from deconsolidation					$ 5,500
HMN
Business Acquisition [Line Items]
Consideration to be received							$ 285,000
ICS | Discontinued Operations
Business Acquisition [Line Items]
Gain (loss) on sale of subsidiary			$ 900
Foreign currency translation adjustment			$ 8,200
Beyond6
Business Acquisition [Line Items]
Consideration to be received		$ 106,500
Proceeds from divestiture of businesses		70,000
Beyond6 | Discontinued Operations
Business Acquisition [Line Items]
Gain (loss) on sale of subsidiary		$ 39,200						$ 500
DTV America
Business Acquisition [Line Items]
Parents interest, controlling (approximately)								76.00%		60.00%				76.00%
Minority Holders
Business Acquisition [Line Items]
Percentage of proxy and voting rights from minority holders								10.00%		10.00%				10.00%
New Saxon 2019 Limited
Business Acquisition [Line Items]
Parents interest, controlling (approximately)				19.00%		73.00%
GMSL
Business Acquisition [Line Items]
Parents interest, controlling (approximately)				30.00%			49.00%	73.00%						73.00%
Number of payment tranches | tranche							2
HMN
Business Acquisition [Line Items]
Ownership percentage before sale of stock							49.00%