Investment in Securities, Investment in Equity Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Investments in Equity Securities and Funds [Abstract]
Cost	$ 49,439	$ 47,726
Estimated Fair Value	30,430	25,845
Common Stock [Member]
Investments in Equity Securities and Funds [Abstract]
Cost	38,297	41,341
Estimated Fair Value	19,068	19,099
Open-end Funds [Member]
Investments in Equity Securities and Funds [Abstract]
Cost	5,632	5,757
Estimated Fair Value	5,960	6,128
Actively Managed Semi-transparent EFTs [Member]
Investments in Equity Securities and Funds [Abstract]
Cost	5,000	0
Estimated Fair Value	4,890	0
Closed-end Funds [Member]
Investments in Equity Securities and Funds [Abstract]
Cost	510	628
Estimated Fair Value	$ 512	$ 618