Investments in Securities and Fair Value Investments in Securities (Schedule of Carrying Value and Fair Value of Financial Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financial Assets
Cash	$ 25,949	$ 18,694
Accrued interest and dividends	1,033	946
Equity securities, at fair value	61,108	48,489
Money market funds and certificates of deposit	13,134	32,787
Equity investments in unconsolidated affiliates, equity method	6,083	5,847
Equity investments in unconsolidated affiliates, measurement alternative	7,899	6,589	$ 5,439
Assets, Fair Value Disclosure	115,206	113,352
Level 1
Financial Assets
Cash	25,949	18,694
Accrued interest and dividends	1,033	946
Equity securities, at fair value	61,108	48,489
Money market funds and certificates of deposit	13,134	32,787
Equity investments in unconsolidated affiliates, equity method	0	0
Equity investments in unconsolidated affiliates, measurement alternative	0	0
Assets, Fair Value Disclosure	101,224	100,916
Level 2
Financial Assets
Cash	0	0
Accrued interest and dividends	0	0
Equity securities, at fair value	0	0
Money market funds and certificates of deposit	0	0
Equity investments in unconsolidated affiliates, equity method	0	0
Equity investments in unconsolidated affiliates, measurement alternative	0	0
Assets, Fair Value Disclosure	0	0
Level 3
Financial Assets
Cash	0	0
Accrued interest and dividends	0	0
Equity securities, at fair value	0	0
Money market funds and certificates of deposit	0	0
Equity investments in unconsolidated affiliates, equity method	6,083	5,847
Equity investments in unconsolidated affiliates, measurement alternative	7,899	6,589
Assets, Fair Value Disclosure	$ 13,982	$ 12,436