Business Segment Information - Selected Financial Data for the Company's Business Segment Information (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenue		$ 389.5	$ 382.5	$ 1,149.5	$ 1,146.3
Operating income (loss)		24.7	22.8	32.2	57.8
Expenditures for long-lived assets	[1]	61.5	56.7	160.9	167.3
Depreciation and amortization		71.9	75.5	220.8	229.1
Assets		2,563.8		2,563.8		$ 2,653.8
Operating Segments [Member] | Entertainment and Communications [Member]
Segment Reporting Information [Line Items]
Revenue		241.0	248.5	724.5	749.3
Operating income (loss)		27.2	27.7	69.8	81.2
Expenditures for long-lived assets	[1]	57.6	51.3	144.2	150.3
Depreciation and amortization		61.6	64.4	190.0	190.5
Assets		1,788.0		1,788.0		1,840.0
Operating Segments [Member] | IT Services and Hardware [Member]
Segment Reporting Information [Line Items]
Revenue		155.2	140.5	444.5	417.0
Operating income (loss)		4.6	0.6	11.5	(5.1)
Expenditures for long-lived assets	[1]	3.9	5.4	16.7	16.9
Depreciation and amortization		10.2	11.1	30.7	38.5
Assets		447.5		447.5		500.7
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenue		(6.7)	(6.5)	(19.5)	(20.0)
Intersegment Elimination [Member] | Entertainment and Communications [Member]
Segment Reporting Information [Line Items]
Revenue		4.9	5.3	14.8	16.5
Intersegment Elimination [Member] | IT Services and Hardware [Member]
Segment Reporting Information [Line Items]
Revenue		1.8	1.2	4.7	3.5
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)		(7.1)	(5.5)	(49.1)	(18.3)
Expenditures for long-lived assets	[1]	0.0	0.0	0.0	0.1
Depreciation and amortization		0.1	0.0	0.1	0.1
Corporate and Elimination [Member]
Segment Reporting Information [Line Items]
Assets		328.3		328.3		$ 313.1
Sales [Member] | Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenue		$ 6.7	$ 6.5	$ 19.5	$ 20.0

[1] Includes deposit for the purchase of wireless licenses