Marketable Securities - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Marketable securities, realized gain	$ 14	$ 174	$ 290	$ 268
Marketable securities, realized loss	$ 6	$ 0	$ 878	$ 147