Quarterly report pursuant to Section 13 or 15(d)

Fair Value - Schedule of Fair Value of Financial Assets and Liabilities Inputs (Details)

v3.10.0.1
Fair Value - Schedule of Fair Value of Financial Assets and Liabilities Inputs (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Assets    
Assets measured at fair value $ 252,780  
Money market funds    
Assets    
Assets measured at fair value 51,273  
Commercial paper    
Assets    
Assets measured at fair value 170,302  
Certificates of deposit    
Assets    
Assets measured at fair value 7,504  
Corporate debt securities    
Assets    
Assets measured at fair value 19,204  
U.S. government and government agency debt securities    
Assets    
Assets measured at fair value 4,497  
Recurring measurement    
Assets    
Total assets measured at fair value 252,780 $ 354,553
Recurring measurement | Money market funds    
Assets    
Money market funds 51,273 353,303
Recurring measurement | Commercial paper    
Assets    
Assets measured at fair value 170,302  
Recurring measurement | Certificates of deposit    
Assets    
Assets measured at fair value 7,504  
Recurring measurement | Corporate debt securities    
Assets    
Assets measured at fair value 19,204 1,250
Recurring measurement | U.S. government and government agency debt securities    
Assets    
Assets measured at fair value 4,497  
Recurring measurement | Quoted Prices in Active Markets for Identical Instruments (Level 1)    
Assets    
Total assets measured at fair value 51,273 353,303
Recurring measurement | Quoted Prices in Active Markets for Identical Instruments (Level 1) | Money market funds    
Assets    
Money market funds 51,273 353,303
Recurring measurement | Quoted Prices in Active Markets for Identical Instruments (Level 1) | Commercial paper    
Assets    
Assets measured at fair value 0  
Recurring measurement | Quoted Prices in Active Markets for Identical Instruments (Level 1) | Certificates of deposit    
Assets    
Assets measured at fair value 0  
Recurring measurement | Quoted Prices in Active Markets for Identical Instruments (Level 1) | Corporate debt securities    
Assets    
Assets measured at fair value 0 0
Recurring measurement | Quoted Prices in Active Markets for Identical Instruments (Level 1) | U.S. government and government agency debt securities    
Assets    
Assets measured at fair value 0  
Recurring measurement | Significant Other Observable Inputs (Level 2)    
Assets    
Total assets measured at fair value 201,507 1,250
Recurring measurement | Significant Other Observable Inputs (Level 2) | Money market funds    
Assets    
Money market funds 0 0
Recurring measurement | Significant Other Observable Inputs (Level 2) | Commercial paper    
Assets    
Assets measured at fair value 170,302  
Recurring measurement | Significant Other Observable Inputs (Level 2) | Certificates of deposit    
Assets    
Assets measured at fair value 7,504  
Recurring measurement | Significant Other Observable Inputs (Level 2) | Corporate debt securities    
Assets    
Assets measured at fair value 19,204 $ 1,250
Recurring measurement | Significant Other Observable Inputs (Level 2) | U.S. government and government agency debt securities    
Assets    
Assets measured at fair value $ 4,497