Quarterly report pursuant to Section 13 or 15(d)

Cash Equivalents and Marketable Securities - Schedule of Cash Equivalents and Marketable Securities (Details)

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Cash Equivalents and Marketable Securities - Schedule of Cash Equivalents and Marketable Securities (Details) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Jun. 30, 2018
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis $ 165,833 $ 195,443  
Unrealized Gains 212    
Unrealized Losses   (47)  
Fair Value 166,045 195,396  
Less amounts classified as cash equivalents, Amortized Cost Basis (19,390) (125,298) $ (25,420)
Marketable Securities      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 148,624 79,241  
Unrealized Gains 212    
Unrealized Losses   (47)  
Fair Value 148,836 79,194  
Cash Equivalents      
Cash And Cash Equivalents [Line Items]      
Less amounts classified as cash equivalents, Amortized Cost Basis (17,209) (116,202)  
Less amounts classified as cash equivalents, Fair Value (17,209) (116,202)  
Money Market Funds      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 17,209 116,202  
Unrealized Gains 0    
Unrealized Losses   0  
Fair Value 17,209 116,202  
Commercial Paper      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 38,810 26,625  
Unrealized Gains 0    
Unrealized Losses   0  
Fair Value 38,810 26,625  
Corporate Debt Securities      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 50,517 11,795  
Unrealized Gains 92    
Unrealized Losses   (21)  
Fair Value 50,609 11,774  
Asset-backed Securities      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 32,447 16,920  
Unrealized Gains 68    
Unrealized Losses   (21)  
Fair Value 32,515 16,899  
U.S. Government Agencies      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 26,850 23,901  
Unrealized Gains 52    
Unrealized Losses   (5)  
Fair Value $ 26,902 $ 23,896