Consolidated Financial Statement Components - Depreciation, Amortization and Accretion (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation	$ 2,076	$ 2,057
Amortization	1,007	1,111
Accretion	140	155
Total depreciation, amortization and accretion expense	3,223	3,323
Leasehold improvements
Property, Plant and Equipment [Line Items]
Depreciation	50	45
Asset retirement costs
Property, Plant and Equipment [Line Items]
Depreciation	(98)	(70)
Paging and computer equipment
Property, Plant and Equipment [Line Items]
Depreciation	2,059	2,002
Furniture, fixtures and vehicles
Property, Plant and Equipment [Line Items]
Depreciation	$ 65	$ 80