Financial Statement Components - Components of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Prepaid Expense And Other Assets Current [Abstract]
Prepaid expenses	$ 13,690	$ 9,780
Inventory	198	63
Other current assets	7,624	5,470
Total prepaid expenses and other current assets	$ 21,512	$ 15,313