Investments in Securities and Fair Value Investments in Securities (Schedule of Cost-method Investments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Measurement Alternative Investments
Beginning of Period	$ 7,899	$ 6,589
Amounts Impairment	0	0
Observable Changes	0	0
Purchases and Additional Commitments Paid	1,227	2,241
Sales, Returns of Capital, and Other Reductions	(385)	(931)
End of Period	$ 8,741	$ 7,899