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TAXABLE INCOME AND TAX BASIS (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
TAXABLE INCOME AND TAX BASIS      
Excess amount of statement income over taxable income     $ 1,500,000
Excess amount of cumulative statement basis over cumulative taxable basis     1,532,000
Excess amount of statement income from joint venture investments over taxable income     5,000,000
Reconciliation of GAAP net income to taxable income      
Financial statement ("book") net income $ 1,878,558 $ 1,894,234  
Reconciliation of Income from Book Basis to Tax Basis Profit (Loss) Tax Basis     $ 5,438,000