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Related Party Transactions - Narratives - Terra International 3 (Details) - USD ($)		3 Months Ended	9 Months Ended
	Apr. 29, 2020	Mar. 31, 2020	Sep. 30, 2019	Mar. 02, 2020	Dec. 31, 2019
Related Party Transaction
Participating Mortgage Loans, Participation Liabilities, Amount		$ 67,700,000		$ 49,800,000	$ 103,200,000
Equity Method Investment, Ownership Percentage		90.00%
TPT 2 and TIF 3 REIT
Related Party Transaction
Participating Mortgage Loans, Participation Liabilities, Amount		$ 49,800,000.0
Terra International Fund 3
Related Party Transaction
Proceeds from Contributed Capital			$ 3,600,000.0
Investment Owned, Balance, Shares			212,691
Investment Company, Investment Income (Loss), Per Share			$ 17.02
Income (Loss) from Discontinued Operations, Net of Tax, Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted		$ 50,000
Terra Fund 5
Related Party Transaction
Investment Company, Contributed Capital to Committed Capital Ratio		87.60%
Terra Fund 7
Related Party Transaction
Investment Company, Contributed Capital to Committed Capital Ratio		12.40%
Forecast
Related Party Transaction
Stock Redeemed or Called During Period, Shares	212,691