Investments - Investments, Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity Investments, at Fair Value, Cost	$ 21,368	$ 34,789
Equity Investments, at Fair Value, Unrealized Gain/(Loss)	(30)	(569)
Equity Investments, at Fair Value	21,338	34,220
Trading Securities, Amortized Cost	8,983	5,283
Trading Securities Unrealized Gain Loss	22
Total Trading Securities	9,005	5,283
Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity Investments, at Fair Value, Cost	14,523	10,112
Equity Investments, at Fair Value, Unrealized Gain/(Loss)	(57)	(545)
Equity Investments, at Fair Value	14,466	9,567
Mutual Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity Investments, at Fair Value, Cost	6,845	24,677
Equity Investments, at Fair Value, Unrealized Gain/(Loss)	27	(24)
Equity Investments, at Fair Value	6,872	24,653
U.S. Treasury Bills
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading Securities, Amortized Cost	8,983	5,283
Trading Securities Unrealized Gain Loss	22
Total Trading Securities	$ 9,005	$ 5,283