Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Financial Assets measured at Fair Value on a Recurring Basis (Details)

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Fair Value Measurements - Financial Assets measured at Fair Value on a Recurring Basis (Details) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity securities, estimated fair value   $ 588
Assets, fair value disclosure   31,813
Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure   31,813
Available-for-sale Securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity securities, estimated fair value   588
Available-for-sale Securities | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity securities, estimated fair value   588
Money market funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents, estimated fair value $ 71,248 31,225
Money market funds | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents, estimated fair value $ 71,248 $ 31,225