Consolidated Financial Statement Components - Depreciation, Amortization and Accretion (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation	$ 1,953	$ 2,076
Amortization	625	1,007
Accretion	135	140
Total depreciation, amortization and accretion expense	2,713	3,223
Leasehold improvements
Property, Plant and Equipment [Line Items]
Depreciation	68	50
Asset retirement costs
Property, Plant and Equipment [Line Items]
Depreciation	(76)	(98)
Paging and computer equipment
Property, Plant and Equipment [Line Items]
Depreciation	1,855	2,044
Furniture, fixtures and vehicles
Property, Plant and Equipment [Line Items]
Depreciation	$ 106	$ 80