Schedule IV - Mortgage Loans on Commercial Real Estate (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Face amount	$ 568,385
Loans	498,081
Mezzanine debt investments | Retail | Massachusetts
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	61,329
Face amount	10,000
Loans	$ 0
Interest rate	10.14%
Mezzanine debt investments | Retail | Ohio
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 124,750
Face amount	36,603
Loans	$ 0
Interest rate	9.50%
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	3,436
Loans	$ 3,405
Mezzanine debt investments | Retail | Colorado | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
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	1.20%
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	3,292
Loans	$ 2,684
Mezzanine debt investments | Retail | North Carolina | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
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
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 60,212
Face amount	8,700
Loans	$ 8,258
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	$ 0
Face amount	19,436
Loans	$ 19,064
Mezzanine debt investments | Office | Texas | Group One | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.75%
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	15,000
Loans	$ 14,884
Mezzanine debt investments | Office | Texas | Group Two | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.45%
Mezzanine debt investments | 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%
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	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	$ 0
Face amount	23,013
Loans	$ 23,012
Interest rate	0.16%
Mezzanine debt investments | Office | California | Group One | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	4.84%
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
Interest rate	0.16%
Mezzanine debt investments | Office | California | Group Two | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	6.79%
Mezzanine debt investments | Office | California | Group Three
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	8,415
Loans	$ 8,351
Mezzanine debt investments | Office | California | Group Three | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.00%
Mezzanine debt investments | Office | California | Minimum | Group Three
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.50%
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	$ 18,052
Mezzanine debt investments | Office | Florida | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
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	1.90%
Mezzanine debt investments | Office | New Jersey
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	9,922
Loans	$ 9,369
Interest rate	0.25%
Mezzanine debt investments | Office | New Jersey | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	10.48%
Mezzanine debt investments | Hotel | Louisiana
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 81,200
Face amount	14,800
Loans	$ 6,796
Interest rate	0.16%
Mezzanine debt investments | Hotel | Louisiana | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	9.75%
First mortgages | Retail | California
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	40,029
Loans	$ 35,356
First mortgages | Retail | California | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.40%
First mortgages | Retail | California | Minimum
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
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	393
Loans	$ 330
First mortgages | Retail | North Carolina | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.40%
First mortgages | Retail | North Carolina | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.25%
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	67,281
Loans	$ 66,169
First mortgages | Office | Texas | Group One | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.75%
First mortgages | 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	12,000
Loans	$ 11,907
First mortgages | Office | Texas | Group Two | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.45%
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 | Texas | Minimum | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	2.25%
First mortgages | Office | Florida
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	85,067
Loans	$ 84,443
First mortgages | Office | Florida | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.00%
First mortgages | Office | Florida | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.50%
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	53,968
Loans	$ 50,956
First mortgages | Office | New Jersey | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.40%
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 | Hotel | Texas
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	8,038
Loans	$ 7,827
First mortgages | Hotel | Texas | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.75%
First mortgages | Hotel | Texas | Minimum
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
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	15,874
Loans	$ 14,641
First mortgages | Industrial | North Carolina | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	2.85%
First mortgages | Industrial | North Carolina | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.85%
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	15,212
Loans	$ 14,872
First mortgages | Industrial | Arizona | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
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 | 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	$ 31,257
First mortgages | Multifamily | Delaware | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	2.90%
First mortgages | Multifamily | Delaware | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.75%
First mortgages | Multifamily | New York | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	37,403
Loans	$ 36,062
First mortgages | Multifamily | New York | Group One | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.25%
First mortgages | Multifamily | New York | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	238
Loans	$ 232
First mortgages | Multifamily | New York | Group Two | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.25%
First mortgages | Multifamily | New York | Minimum | Group One
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.75%
First mortgages | Multifamily | New York | Minimum | Group Two
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.75%
First mortgages | Healthcare | Washington
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior liens	$ 0
Face amount	20,152
Loans	$ 19,873
First mortgages | Healthcare | Washington | LIBOR
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable interest rate	3.40%
First mortgages | Healthcare | Washington | Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate	1.75%