Fair Value of Financial Instruments - Fair value, unrealized gains (losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 14,198	$ 20,046
Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost	20,596	20,596
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6,398)	(550)
Fair Value	$ 14,198	$ 20,046