Investments in Securities and Fair Value Investments in Securities (Schedule of Equity Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, cost	$ 33,570	$ 31,255
Equity securities, at fair value	61,108	48,489
Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, cost	33,570	31,255
Equity securities, at fair value	$ 61,108	$ 48,489