Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)

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Fair Value Measurements Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2019
USD ($)
Sep. 30, 2019
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable security gains (losses), net $ (100) $ 300
Fair Value, Measurements, Recurring | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash, cash equivalents, restricted cash and restricted cash equivalents 78,036 78,036
Marketable securities 6,038 6,038
Construction reserve funds 3,908 3,908
Fair Value, Measurements, Recurring | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash, cash equivalents, restricted cash and restricted cash equivalents 0 0
Marketable securities 0 0
Construction reserve funds 0 0
Fair Value, Measurements, Recurring | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash, cash equivalents, restricted cash and restricted cash equivalents 0 0
Marketable securities 0 0
Construction reserve funds $ 0 $ 0