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Balance Sheet Components - Summary of Amortized Cost, Gross Unrealized Holding Gains or Losses, and Fair Value of Available-for-Sale Investments (Detail) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 38,599 $ 71,360
Gross Unrealized Holding Gains 120 1,252
Gross Unrealized Holding Losses (38) (46)
Fair Value 38,681 72,566
Corporate bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 28,132 53,985
Gross Unrealized Holding Gains 0 4
Gross Unrealized Holding Losses (38) (46)
Fair Value 28,094 53,943
Bond and mutual funds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 10,341 17,249
Gross Unrealized Holding Gains 36 1,153
Gross Unrealized Holding Losses 0 0
Fair Value 10,377 18,402
Equity investments [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 126 126
Gross Unrealized Holding Gains 84 95
Gross Unrealized Holding Losses 0 0
Fair Value $ 210 $ 221