Schedule IV - Mortgage Loans on Commercial Real Estate (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Face amount	$ 686,563
Loans	669,713
Mezzanine debt investments | Retail | Massachusetts
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	62,053
Face amount	10,000
Loans	$ 10,000
Interest rate	10.14%
Mezzanine debt investments | Retail | Colorado
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	470
Loans	$ 470
Basis spread on variable interest rate	5.00%
Mezzanine debt investments | Retail | Colorado | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	0.50%
Mezzanine debt investments | Retail | Washington, DC
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	17,100
Loans	$ 17,100
Basis spread on variable interest rate	7.73%
Mezzanine debt investments | Retail | Washington, DC | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	0.50%
Mezzanine debt investments | Retail | North Carolina
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	2,692
Loans	$ 2,668
Basis spread on variable interest rate	3.40%
Mezzanine debt investments | Retail | North Carolina | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.25%
Mezzanine debt investments | Office | Louisiana | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 60,989
Face amount	8,700
Loans	$ 8,700
Interest rate	10.75%
Mezzanine debt investments | Office | Texas | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 50,420
Face amount	7,000
Loans	$ 0
Interest rate	10.10%
Mezzanine debt investments | Office | Texas | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	19,136
Loans	$ 18,992
Basis spread on variable interest rate	3.75%
Mezzanine debt investments | Office | Texas | Group Three
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	15,000
Loans	$ 14,892
Basis spread on variable interest rate	3.45%
Mezzanine debt investments | Office | Texas | Minimum | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.25%
Mezzanine debt investments | Office | Texas | Minimum | Group Three
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.25%
Mezzanine debt investments | Office | California | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 104,682
Face amount	23,013
Loans	$ 23,013
Basis spread on variable interest rate	5.79%
Mezzanine debt investments | Office | California | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 104,682
Face amount	10,281
Loans	$ 10,281
Basis spread on variable interest rate	6.54%
Mezzanine debt investments | Office | Florida
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	18,363
Loans	$ 18,301
Basis spread on variable interest rate	3.30%
Mezzanine debt investments | Office | Florida | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	0.50%
Mezzanine debt investments | Mixed Use | Ohio
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 126,577
Face amount	36,603
Loans	$ 30,900
Interest rate	9.50%
Mezzanine debt investments | Hotel | Louisiana | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 95,588
Face amount	14,706
Loans	$ 14,706
Basis spread on variable interest rate	9.50%
First mortgages | Washington
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	19,044
Loans	$ 18,874
Basis spread on variable interest rate	3.40%
First mortgages | Washington | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.75%
First mortgages | Retail | Texas | Group Four
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	12,000
Loans	$ 11,913
Basis spread on variable interest rate	3.45%
First mortgages | Retail | Texas | Minimum | Group Four
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.25%
First mortgages | Retail | California | Group Four
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	65,366
Loans	$ 64,775
Basis spread on variable interest rate	3.40%
First mortgages | Retail | California | Minimum | Group Four
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.06%
First mortgages | Retail | North Carolina | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	9,390
Loans	$ 9,319
Basis spread on variable interest rate	3.40%
First mortgages | Retail | North Carolina | Minimum | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.25%
First mortgages | Retail | Tennessee | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	85
Loans	$ 89
Basis spread on variable interest rate	4.50%
First mortgages | Retail | Tennessee | Minimum | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.20%
First mortgages | Retail | Delaware
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	31,469
Loans	$ 31,180
Basis spread on variable interest rate	2.90%
First mortgages | Retail | Delaware | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.75%
First mortgages | Office | Texas | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	65,081
Loans	$ 64,673
Basis spread on variable interest rate	3.75%
First mortgages | Office | Texas | Minimum | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.25%
First mortgages | Office | California
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	417
Loans	$ 422
Basis spread on variable interest rate	3.25%
First mortgages | Office | California | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	2,320
Loans	$ 2,320
Basis spread on variable interest rate	3.50%
First mortgages | Office | California | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.00%
First mortgages | Office | California | Minimum | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.00%
First mortgages | Office | Colorado
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	1,868
Loans	$ 1,901
Basis spread on variable interest rate	3.60%
First mortgages | Office | Colorado | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.00%
First mortgages | Office | New Jersey
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	64,390
Loans	$ 64,390
Basis spread on variable interest rate	4.50%
First mortgages | Office | New Jersey | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	0.25%
First mortgages | Office | Virginia | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	33,498
Loans	$ 33,284
Basis spread on variable interest rate	4.00%
First mortgages | Office | Virginia | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	43,100
Loans	$ 42,873
Basis spread on variable interest rate	2.80%
First mortgages | Office | Virginia | Minimum | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.25%
First mortgages | Office | Virginia | Minimum | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.90%
First mortgages | Office | New York
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	16,100
Loans	$ 15,805
Basis spread on variable interest rate	4.60%
First mortgages | Office | New York | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.30%
First mortgages | Hotel | Texas | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	1,288
Loans	$ 1,305
Basis spread on variable interest rate	3.75%
First mortgages | Hotel | Texas | Minimum | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.00%
First mortgages | Industrial | North Carolina | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	47,813
Loans	$ 47,268
Basis spread on variable interest rate	2.85%
First mortgages | Industrial | North Carolina | Minimum | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.85%
First mortgages | Industrial | Tennessee | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	21,250
Loans	$ 21,132
Basis spread on variable interest rate	3.00%
First mortgages | Industrial | Tennessee | Minimum | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.00%
First mortgages | Industrial | Arizona
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	14,300
Loans	$ 14,041
Basis spread on variable interest rate	3.50%
First mortgages | Industrial | Arizona | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.60%
First mortgages | Multifamily | Texas | Group Three
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	70
Loans	$ 70
Basis spread on variable interest rate	2.90%
First mortgages | Multifamily | Texas | Minimum | Group Three
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.25%
First mortgages | Multifamily | California | Group Three
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	350
Loans	$ 350
Basis spread on variable interest rate	3.00%
First mortgages | Multifamily | California | Minimum | Group Three
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.40%
First mortgages | Multifamily | New York
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	54,300
Loans	$ 53,706
Basis spread on variable interest rate	3.25%
First mortgages | Multifamily | New York | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.75%