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Balance Sheet Components - Schedule of Cash and Cash Equivalents (Detail) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Cash And Cash Equivalents [Abstract]        
Cash $ 103,716 $ 79,239    
Money market funds 569,942 94,543    
Total cash and cash equivalents $ 673,658 $ 173,782 $ 153,324 $ 165,455