Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Details)

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Fair Value Measurements - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value Measurements Recurring - USD ($)
$ in Thousands
Jun. 30, 2020
Dec. 31, 2019
Assets:    
Total $ 253,985 $ 131,664
Level 1    
Assets:    
Total 63,229 3,151
Level 2    
Assets:    
Total 190,756 128,513
Money Market Funds    
Assets:    
Total 63,229 3,151
Money Market Funds | Level 1    
Assets:    
Total 63,229 3,151
Commercial Paper    
Assets:    
Total 34,901 4,952
Commercial Paper | Level 2    
Assets:    
Total 34,901 4,952
Corporate Debt Securities    
Assets:    
Total 61,284 69,499
Corporate Debt Securities | Level 2    
Assets:    
Total 61,284 69,499
Equity Securities    
Assets:    
Total 49,094  
Equity Securities | Level 2    
Assets:    
Total 49,094  
Asset-backed Securities    
Assets:    
Total 16,217 27,055
Asset-backed Securities | Level 2    
Assets:    
Total 16,217 27,055
U.S. Government Agency Securities    
Assets:    
Total 29,260 27,007
U.S. Government Agency Securities | Level 2    
Assets:    
Total $ 29,260 $ 27,007