Marketable Securities - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Marketable securities, realized gains	$ 474	$ 483	$ 317
Marketable securities, realized loss	$ 912	$ 151	$ 565