Investments in Securities and Fair Value (Schedule of Carrying Value and Fair Value of Financial Assets Disclosed) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 30,411	$ 35,311
Accrued interest and dividends	1,111	872
Equity securities, estimated fair value	31,831	51,691
Money market funds and U.S. Treasury bills	103,959	103,649
Assets, fair value disclosure	167,312	191,523
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	30,411	35,311
Accrued interest and dividends	1,111	872
Equity securities, estimated fair value	31,831	51,691
Money market funds and U.S. Treasury bills	103,959	103,649
Assets, fair value disclosure	167,312	191,523
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Accrued interest and dividends	0	0
Equity securities, estimated fair value	0	0
Money market funds and U.S. Treasury bills	0	0
Assets, fair value disclosure	0	0
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Accrued interest and dividends	0	0
Equity securities, estimated fair value	0	0
Money market funds and U.S. Treasury bills	0	0
Assets, fair value disclosure	$ 0	$ 0