Investments in Securities and Fair Value Investments in Securities (Schedule of Equity Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, cost	$ 31,255	$ 26,003
Gross unrealized gains		21,376
Gross unrealized losses		12
Equity securities, at fair value	48,489	47,367
Common Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, cost	31,255	26,003
Gross unrealized gains		21,376
Gross unrealized losses		12
Equity securities, at fair value	$ 48,489	$ 47,367