Consolidated Financial Statements' Components - Property and Equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 99,126	$ 103,470
Accumulated depreciation	(92,380)	(95,655)
Total property and equipment, net	$ 6,746	7,815
Minimum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	1 year
Maximum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	5 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,307	3,628
Asset retirement costs
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 2,307	3,717
Asset retirement costs | Minimum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	1 year
Asset retirement costs | Maximum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	5 years
Paging and computer equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 89,844	92,608
Paging and computer equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	1 year
Paging and computer equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	5 years
Furniture, fixtures and vehicles
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,668	$ 3,517
Furniture, fixtures and vehicles | Minimum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	3 years
Furniture, fixtures and vehicles | Maximum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	5 years