Annual report pursuant to Section 13 and 15(d)

SCHEDULE IV - MORTGAGE LOANS ON REAL ESTATE - Mortgage Loans On Real Estate (Details)

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SCHEDULE IV - MORTGAGE LOANS ON REAL ESTATE - Mortgage Loans On Real Estate (Details) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]        
Face Value $ 1,300,000      
Carrying Amount of Mortgage 1,235,000 $ 1,300,000 $ 1,500,000 $ 1,500,000
Principal Amount of Loans Subject to Delinquent Principal or Interest $ 0      
Billings, Dunn and McKenzie Counties, North Dakota (Morlock Well) | First Mortgages        
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]        
Interest Rate 8.50%      
Monthly Payment Amount $ 10,833      
Face Value 1,300,000      
Carrying Amount of Mortgage 1,235,000      
Principal Amount of Loans Subject to Delinquent Principal or Interest $ 0