Consolidated Financial Statement Components - Depreciation, Amortization and Accretion (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Property, Plant and Equipment [Line Items]
Depreciation	$ 2,082	$ 2,044	$ 4,158	$ 4,101
Amortization	629	1,035	1,636	2,146
Accretion	140	156	280	311
Total depreciation, amortization and accretion expense	2,851	3,235	6,074	6,558
Leasehold improvements
Property, Plant and Equipment [Line Items]
Depreciation	75	52	125	98
Asset retirement costs
Property, Plant and Equipment [Line Items]
Depreciation	(97)	(69)	(195)	(140)
Paging and computer equipment
Property, Plant and Equipment [Line Items]
Depreciation	2,028	1,992	4,087	3,995
Furniture, fixtures and vehicles
Property, Plant and Equipment [Line Items]
Depreciation	$ 76	$ 69	$ 141	$ 148