Fair Value Measurements - Summary of Financial Assets and Liabilities Recognized at Fair Value On a Recurring Basis (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	$ 138,063,017	$ 132,964,276
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	138,063,017	132,964,276
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	138,063,017	132,964,276
Fair Value, Measurements, Recurring [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	4,498,937	5,377,522
Fair Value, Measurements, Recurring [Member] | Preferred Stock [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	4,498,937	5,377,522
Fair Value, Measurements, Recurring [Member] | Preferred Stock [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Fair Value, Measurements, Recurring [Member] | Preferred Stock [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Fair Value, Measurements, Recurring [Member] | Common Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	133,564,080	127,586,754
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	133,564,080	127,586,754
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	0	0
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities	$ 0	$ 0