Loans Held for Investment - Loan Portfolio (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan	Mar. 31, 2020 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	14	12
Carrying value | $	$ 278,225	$ 242,078	$ 271,487
Percentage of Value	100.00%	100.00%
East
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	5	4
Carrying value | $	$ 104,461	$ 90,047
Percentage of Value	37.00%	37.00%
South
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	5	5
Carrying value | $	$ 105,385	$ 103,295
Percentage of Value	38.00%	43.00%
West
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	1	1
Carrying value | $	$ 10,503	$ 9,014
Percentage of Value	4.00%	4.00%
Midwest
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	3	2
Carrying value | $	$ 57,876	$ 39,722
Percentage of Value	21.00%	16.00%
Office
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	5	4
Carrying value | $	$ 90,427	$ 71,446
Percentage of Value	32.00%	30.00%
Hotel
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	1	1
Carrying value | $	$ 23,848	$ 23,101
Percentage of Value	9.00%	10.00%
Retail
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	3	3
Carrying value | $	$ 45,676	$ 43,782
Percentage of Value	16.00%	18.00%
Multifamily
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	3	3
Carrying value | $	$ 69,391	$ 68,911
Percentage of Value	25.00%	28.00%
Industrial
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans | loan	2	1
Carrying value | $	$ 48,883	$ 34,838
Percentage of Value	18.00%	14.00%