Business Segment Information (Details) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments										2	2	2
Increases (Decreases) in Total Assets										$ 542.6
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent		$ 47.5				$ 12.2				47.5	$ 12.2
Deferred Tax Liabilities, Net, Noncurrent		11.4				11.2				11.4	11.2
Revenue		399.0	$ 386.7	$ 296.8	$ 295.7	301.2	$ 255.5	$ 259.4	$ 249.6	1,378.2	1,065.7	$ 1,017.6
Operating income		24.4	14.5	$ 20.2	$ 24.2	16.9	$ 15.9	$ 24.4	$ (1.8)	83.3	55.4	98.8
Expenditures for long-lived assets										220.6	210.5	286.4
Depreciation and amortization										252.0	193.0	182.2
Assets		2,730.2				2,187.6				2,730.2	2,187.6
Entertainment and Communications [Member]
Segment Reporting Information [Line Items]
Increases (Decreases) in Total Assets										787.4
Revenue										853.4	706.1	691.3
Operating income										103.3	86.1	100.1
Expenditures for long-lived assets											186.3	260.8
Depreciation and amortization										210.8	163.7	159.1
Assets		1,898.8				1,111.4				1,898.8	1,111.4
IT Services and Hardware [Member]
Segment Reporting Information [Line Items]
Increases (Decreases) in Total Assets										(14.6)
Revenue										550.9	385.1	352.7
Operating income										17.2	5.3	17.4
Expenditures for long-lived assets												25.4
Depreciation and amortization										41.0	29.1	23.0
Assets		468.1				482.7				468.1	482.7
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Increases (Decreases) in Total Assets										(230.2)
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent		47.5				12.2				47.5	12.2
Deferred Tax Liabilities, Net, Noncurrent		11.4				11.2				11.4	11.2
Operating income										(37.2)	(36.0)	(18.7)
Expenditures for long-lived assets										0.2	0.0	0.2
Depreciation and amortization										0.2	0.2	0.1
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue										(26.1)	(25.5)	(26.4)
Intersegment Eliminations [Member] | Entertainment and Communications [Member]
Segment Reporting Information [Line Items]
Revenue										22.3	21.2	21.0
Intersegment Eliminations [Member] | IT Services and Hardware [Member]
Segment Reporting Information [Line Items]
Revenue										3.8	4.3	5.4
Intersegment Eliminations [Member] | Corporate Segment [Member]
Segment Reporting Information [Line Items]
Assets		363.3				$ 593.5				363.3	593.5
Sales [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue										26.1	25.5	26.4
Continuing Operations [Member]
Segment Reporting Information [Line Items]
Expenditures for long-lived assets											377.5	286.4
Depreciation and amortization										252.0	193.0	$ 182.2
Expenditures for Long-Lived Assets, Including Acquisitions of Businesses [Member] | Entertainment and Communications [Member]
Segment Reporting Information [Line Items]
Expenditures for long-lived assets	[1]									408.0
Expenditures for Long-Lived Assets, Including Acquisitions of Businesses [Member] | IT Services and Hardware [Member]
Segment Reporting Information [Line Items]
Expenditures for long-lived assets	[1]									29.2	$ 191.2
Expenditures for Long-Lived Assets, Including Acquisitions of Businesses [Member] | Continuing Operations [Member]
Segment Reporting Information [Line Items]
Expenditures for long-lived assets	[1]									437.4
Hawaiian Telcom Holdco, Inc. [Member]
Segment Reporting Information [Line Items]
Revenue Contributed from Acquired Companies		$ 87.9	$ 87.1							$ 159.2

[1] Includes cost of acquisitions