Balance Sheet Components - Components of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities And Other Liabilities [Abstract]
Accrued salary and payroll-related expenses	$ 4,372	$ 3,894
Accrued accounts payable	2,161	1,915
Customer advances	2,003	1,582
Deferred rent	475	408
Sales and use tax payable	341	210
Income taxes payable	142	0
Other	521	353
Accrued expenses and other current liabilities	$ 10,015	$ 8,362