Balance Sheet Components - Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Distribution fees	$ 15,394	$ 18,485
Marketing expenses	2,505	2,826
Prefunded liability	1,723	2,151
Traffic acquisition cost	2,289	3,040
Other	9,986	9,036
Other current liabilities	$ 31,897	$ 35,538