Summary of Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property Plant and Equipment, Gross	$ 142,680	$ 142,403
Accumulated depreciation	(87,795)	(83,692)
Net property and equipment	54,885	58,711
Land and Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment, Gross	14,559	14,693
Building [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment, Gross	$ 38,059	37,984
Estimated Useful Life	31 years 6 months
Towers And Antennae [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment, Gross	$ 25,976	24,762
Towers And Antennae [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Towers And Antennae [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	15 years
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment, Gross	$ 53,547	54,321
Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	15 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment, Gross	$ 7,189	7,169
Furniture and Fixtures [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	7 years
Furniture and Fixtures [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	20 years
Vehicles [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment, Gross	$ 3,350	$ 3,474
Estimated Useful Life	5 years