Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended				19 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Oct. 06, 2017	Oct. 02, 2017	Sep. 30, 2013
Selected Quarterly Financial Information [Abstract]
Revenues	$ 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 (loss) income	24.4	14.5	20.2	24.2	16.9	15.9	24.4	(1.8)	83.3		55.4	98.8
Net income (loss)	$ (30.0)	$ (17.7)	$ (13.8)	$ (8.3)	$ (11.9)	$ (11.0)	$ 2.3	$ 60.6	$ (69.8)		$ 40.0	$ 103.0
Earnings Per Share, Basic	$ (0.65)	$ (0.41)	$ (0.39)	$ (0.26)	$ (0.34)	$ (0.32)	$ (0.01)	$ 1.38	$ (1.73)		$ 0.70	$ 2.20
Earnings Per Share, Diluted	$ (0.65)	$ (0.41)	$ (0.39)	$ (0.26)	$ (0.34)	$ (0.32)	$ (0.01)	$ 1.37	$ (1.73)		$ 0.70	$ 2.20
Transaction and integration cost	$ 4.3	$ 13.3	$ 2.7	$ 2.2	$ 4.1	$ 12.1	$ 1.7	$ 0.6	$ 22.5		$ 18.5	$ 0.0
Interest expense									131.5		85.2	75.7
Marketable Securities, Realized Gain (Loss)								117.7	0.0		117.7	157.0
Loss (Gain) on Extinguishment of Debt			1.3						1.3		3.2	19.0
Condensed Income Statements, Captions [Line Items]
Restructuring and severance related charges	3.4		4.6	0.3	3.5		$ 3.6	$ 25.6	8.3		32.7	$ 11.9
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense					6.8
Hawaiian Telcom Holdco, Inc. [Member]
Selected Quarterly Financial Information [Abstract]
Transaction and integration cost									19.2		8.0		$ 27.2
Condensed Income Statements, Captions [Line Items]
Revenue of acquiree since acquisition date included in consolidated statement of income	87.9	87.1							159.2
Net income of acquiree since acquisition date included in consolidated statement of income	1.2	(0.5)
OnX Holdings LLC [Member]
Selected Quarterly Financial Information [Abstract]
Transaction and integration cost									$ 0.5	$ 8.6	$ 8.1
Condensed Income Statements, Captions [Line Items]
Revenue of acquiree since acquisition date included in consolidated statement of income	59.1	49.3	45.3	45.3	53.0
Net income of acquiree since acquisition date included in consolidated statement of income	$ 2.1	$ (1.0)	$ (4.3)	$ (2.7)	11.5
Tranche B Term Loan due 2024 [Member]
Selected Quarterly Financial Information [Abstract]
Debt Instrument, Face Amount															$ 600.0
8% Senior Notes due 2025 [Member]
Selected Quarterly Financial Information [Abstract]
Debt Instrument, Face Amount														$ 350.0
Tranche B Term Loan due 2020 [Member]
Selected Quarterly Financial Information [Abstract]
Debt Instrument, Face Amount															$ 315.8	$ 540.0
Revolving Credit Facility And Tranche B Term Loan due 2020 [Member]
Selected Quarterly Financial Information [Abstract]
Loss (Gain) on Extinguishment of Debt					$ 3.2