Acquisition - Sprint Territory Expansion (Details) - USD ($) $ in Thousands	Feb. 01, 2018	Sep. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
One-time payment for expansion of service area	$ 52,000
Finite-lived intangible assets	52,000	$ 317,062	$ 316,504
Maximum
Business Acquisition [Line Items]
One-time payment for expansion of service area, additional payment	$ 5,000
Affiliate contract expansion
Business Acquisition [Line Items]
Estimated useful life, finite lived intangible assets	12 years
Finite-lived intangible assets	$ 45,148	302,702	304,193
Prepayment of tangible assets
Business Acquisition [Line Items]
Finite-lived intangible assets	$ 6,497
Off-market leases - favorable
Business Acquisition [Line Items]
Estimated useful life, finite lived intangible assets	16 years 6 months
Finite-lived intangible assets	$ 3,665	$ 14,062	$ 11,881
Off-market leases - unfavorable
Business Acquisition [Line Items]
Estimated useful life, finite lived intangible assets	4 years 2 months 12 days
Finite-lived intangible assets	$ 3,310