Investments - Investments, Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity Investments, at Fair Value, Cost	$ 28,423	$ 4,399
Equity Investments, at Fair Value, Unrealized Gain/(Loss)	587	1,053
Equity Investments, at Fair Value	29,010	5,452
Trading Securities, Amortized Cost	12,954
Trading Securities Unrealized Gain Loss	(3)
Total Trading Securities	12,951	0
Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity Investments, at Fair Value, Cost	6,375	4,399
Equity Investments, at Fair Value, Unrealized Gain/(Loss)	587	1,053
Equity Investments, at Fair Value	6,962	5,452
Mutual Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity Investments, at Fair Value, Cost	22,048
Equity Investments, at Fair Value, Unrealized Gain/(Loss)	0
Equity Investments, at Fair Value	22,048	0
U.S. Treasury Bills
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading Securities, Amortized Cost	11,664
Trading Securities Unrealized Gain Loss	(2)
Total Trading Securities	11,662	0
Corporate Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading Securities, Amortized Cost	1,290
Trading Securities Unrealized Gain Loss	(1)
Total Trading Securities	$ 1,289	$ 0