Fair Value of Financial Instruments Valuation techniques and significant unobservable inputs (Details) - USD ($)	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in private companies, at adjusted cost	$ 3,090,000		$ 4,870,000
Real estate investments, at fair value (cost of $10,225 and 10,225, respectively)	10,662,000		$ 10,662,000	$ 10,662,000
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investments, at fair value (cost of $10,225 and 10,225, respectively)	10,662,000	$ 10,662,000
Common Stock [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in private companies, at adjusted cost	$ 4,124,000.000