Marketable Securities - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Marketable securities, realized gain	$ 136	$ 71	$ 426	$ 339
Marketable securities, realized loss	$ 8	$ 64	$ 886	$ 211