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Balance Sheet Components - Schedule of Cash and Cash Equivalents (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Cash And Cash Equivalents [Abstract]        
Cash $ 69,559 $ 103,716    
Money market funds 589,448 569,942    
Total cash and cash equivalents $ 659,007 $ 673,658 $ 170,598 $ 173,782