Investments in Securities and Fair Value Investments in Securities (Schedule of Equity Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, cost	$ 32,478	$ 33,570
Equity securities, at fair value	64,919	61,108
Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, cost	32,478	33,570
Equity securities, at fair value	$ 64,919	$ 61,108