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Fair Value Measurements - Fair value hierarchy of assets and liabilities (Details) - Recurring - USD ($)
$ in Thousands
Dec. 31, 2021
Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Money market funds $ 37,861 $ 25,855
Equity securities 47,878 3,656
Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Money market funds 37,861 25,855
Equity securities 37,903 3,599
Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Money market funds 0 0
Equity securities 0 0
Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Money market funds 0 0
Equity securities 0 0
Fair Value Measured at Net Asset Value Per Share [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Money market funds 0 0
Equity securities $ 9,975 $ 57