Mergers and Acquisitions - Estimated Fair Value of Identifiable Intangible Assets and Estimated Useful Lives (Details) - USD ($) $ in Millions		Jul. 02, 2018	Sep. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Fair Value	[1]		$ 191.1	$ 190.0
Customer relationships
Business Acquisition [Line Items]
Fair Value	[1]		140.1	139.4
Trade name
Business Acquisition [Line Items]
Fair Value	[1]		$ 41.1	$ 40.7
Hawaiian Telcom Holdco, Inc. [Member]
Business Acquisition [Line Items]
Fair Value		$ 52.0
Hawaiian Telcom Holdco, Inc. [Member] | Customer relationships
Business Acquisition [Line Items]
Fair Value		$ 26.0
Useful Lives		15 years
Hawaiian Telcom Holdco, Inc. [Member] | Trade name
Business Acquisition [Line Items]
Fair Value		$ 26.0
Useful Lives		15 years

[1] Change in gross carrying amounts is due to foreign currency translation on certain intangible assets.