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Balance Sheet Details - Short-Term Investments (Details) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2017
Dec. 31, 2016
Short-term investments    
Amortized cost $ 90,455 $ 89,328
Unrealized gains 30 26
Unrealized losses (65) (86)
Estimated fair value 90,420 89,268
U.S. Government bonds    
Short-term investments    
Amortized cost 1,799  
Unrealized losses (12)  
Estimated fair value $ 1,787  
U.S. Government bonds | Minimum    
Short-term investments    
Maturity 1 year  
U.S. Government bonds | Maximum    
Short-term investments    
Maturity 3 years  
U.S. Government agency bonds    
Short-term investments    
Amortized cost $ 3,697 9,535
Unrealized gains   2
Unrealized losses (12) (22)
Estimated fair value $ 3,685 $ 9,515
U.S. Government agency bonds | Minimum    
Short-term investments    
Maturity   1 year
U.S. Government agency bonds | Maximum    
Short-term investments    
Maturity 3 years 3 years
Bank certificates of deposit    
Short-term investments    
Amortized cost $ 15,450 $ 11,101
Unrealized gains 8 13
Unrealized losses   (1)
Estimated fair value $ 15,458 $ 11,113
Bank certificates of deposit | Maximum    
Short-term investments    
Maturity 1 year 2 years
Commercial paper    
Short-term investments    
Amortized cost $ 8,327 $ 17,011
Unrealized gains 1 1
Unrealized losses   (2)
Estimated fair value $ 8,328 $ 17,010
Commercial paper | Maximum    
Short-term investments    
Maturity 1 year 1 year
Corporate notes    
Short-term investments    
Amortized cost $ 53,435 $ 45,178
Unrealized gains 20 7
Unrealized losses (39) (61)
Estimated fair value $ 53,416 $ 45,124
Corporate notes | Maximum    
Short-term investments    
Maturity 3 years 3 years
Asset-backed securities    
Short-term investments    
Amortized cost $ 7,747 $ 6,503
Unrealized gains 1 3
Unrealized losses (2)  
Estimated fair value $ 7,746 $ 6,506
Asset-backed securities | Maximum    
Short-term investments    
Maturity 2 years 2 years