Consolidated Financial Statement Components - Depreciation, Amortization and Accretion (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Depreciation	$ 8,180	$ 8,570	$ 10,200
Amortization	4,160	4,735	5,722
Accretion	623	665	755
Total depreciation, amortization and accretion expense	12,963	13,970	16,677
Leasehold improvements
Property, Plant and Equipment [Line Items]
Depreciation	189	233	194
Paging and computer equipment
Property, Plant and Equipment [Line Items]
Depreciation	7,974	8,489	9,370
Furniture, fixtures and vehicles
Property, Plant and Equipment [Line Items]
Depreciation	294	353	925
Depreciable life | Asset retirement costs
Property, Plant and Equipment [Line Items]
Depreciation	$ (277)	$ (505)	$ (289)