Investments in Securities and Fair Value (Schedule of Carrying Value and Fair Value of Financial Assets Disclosed) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 29,709	$ 25,949
Accrued interest and dividends	1,005	1,033
Equity Securities, Estimated Fair Value	55,830	61,108
Money market funds and certificates of deposit	24,723	13,134
Equity investments in unconsolidated affiliates, equity method	6,371	6,083
Equity investments in unconsolidated affiliates, measurement alternative	8,509	7,899	$ 6,589
Assets, fair value disclosure	126,147	115,206
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	29,709	25,949
Accrued interest and dividends	1,005	1,033
Equity Securities, Estimated Fair Value	55,830	61,108
Money market funds and certificates of deposit	24,723	13,134
Equity investments in unconsolidated affiliates, equity method	0	0
Equity investments in unconsolidated affiliates, measurement alternative	0	0
Assets, fair value disclosure	111,267	101,224
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 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
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 certificates of deposit	0	0
Equity investments in unconsolidated affiliates, equity method	6,371	6,083
Equity investments in unconsolidated affiliates, measurement alternative	8,509	7,899
Assets, fair value disclosure	$ 14,880	$ 13,982