Discontinued Operations - Narrative (Details) - USD ($) $ in Millions					3 Months Ended					6 Months Ended
	Mar. 29, 2021	Jan. 15, 2021	Oct. 31, 2020	Feb. 28, 2020	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Jan. 30, 2020	Oct. 30, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of subsidiary										$ 40.4	$ (39.3)
Loss on disposal of subsidiary					$ 0.0			$ 0.7		0.0	(22.1)
Repayments of long-term debt										446.1	154.2
Foreign currency translation adjustment					0.4			(3.8)		1.2	(4.0)
Spectrum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Station license					5.2					$ 5.2
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of subsidiary					$ 0.0			0.0			$ (39.3)
CGI
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beneficial ownership interest	6.60%
Transaction value	$ 90.0
Transaction cost including in cash and certain assets at CGI	$ 65.0
CGI | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beneficial ownership interest					6.60%					6.60%
Transaction value					$ 90.0					$ 90.0
Transaction cost including in cash and certain assets at CGI										$ 65.0
Marine Services
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transaction value												$ 250.0	$ 140.0
Transaction cost including in cash and certain assets at CGI				$ 144.0				$ 85.5
Gain (loss) on sale of subsidiary						$ 1.2	$ 2.4		$ (39.3)
Loss on disposal of subsidiary									$ 31.3
Marine Services | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of subsidiary				(39.3)		$ 1.2	$ 2.4
Loss on disposal of subsidiary				31.3
Marine Services | Revolving Credit Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt				15.0
Marine Services | Revolving Credit Agreement | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt				15.0
Marine Services | 11.5% Senior Secured Notes
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt instrument, amount redeemed				$ 76.9
Interest rate				11.50%
Marine Services | Secured Indenture
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt instrument, amount redeemed				$ 76.9
ICS | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of subsidiary			$ 0.9
Foreign currency translation adjustment			$ 8.2
Beyond6
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transaction value		$ 106.5
Transaction cost including in cash and certain assets at CGI		70.0
Gain (loss) on sale of subsidiary		39.2
Beyond6 | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of subsidiary		39.2
Beyond6 | 11.5% Senior Secured Notes
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt		27.9
Beyond6 | 2020 Revolving Credit Agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of long-term debt		$ 15.0