Related Party Arrangements - Equity Plan Grants and Investment Activity (Details) - USD ($) $ in Thousands		1 Months Ended									3 Months Ended		6 Months Ended		12 Months Ended
		Aug. 07, 2020	Jun. 30, 2020	Apr. 30, 2020	Mar. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	May 31, 2018	Mar. 31, 2018	Jul. 31, 2017	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jul. 31, 2019	Jun. 30, 2018
Related Party Transaction [Line Items]
Granted (in shares)													237,340
Outstanding (in shares)			928,230								928,230		928,230		1,335,590
Share-based compensation expense											$ 1,549	$ 2,713	$ 1,891	$ 4,556
Loans and preferred equity held for investment, net	[1]		$ 2,242,574								2,242,574		2,242,574		$ 2,576,332
Unfunded commitment remaining			39,300								39,300		39,300
Face value			2,301,950								2,301,950		2,301,950		2,858,423
Purchase of Class A office campus															127,356
Carrying value			2,908,407								2,908,407		2,908,407		3,188,498
Loan carrying value			2,295,095								2,295,095		$ 2,295,095
Maturity period of debt instruments depending upon the asset type (in years)													3 years 10 months 24 days
Fixed rate
Related Party Transaction [Line Items]
Face value			268,002								268,002		$ 268,002		351,351
Fixed rate | Loans and preferred equity held for investment
Related Party Transaction [Line Items]
Loan carrying value			267,150								267,150		267,150		350,264
Land site and development of office building
Related Party Transaction [Line Items]
Joint venture commitment							$ 69,900
Interest in joint venture (in percentage)							50.00%
Joint venture, total commitment							$ 139,700
Maturity period of debt instruments depending upon the asset type (in years)							3 years 6 months
Mixed-use development project in Ireland
Related Party Transaction [Line Items]
Joint venture commitment						$ 162,400
Interest in joint venture (in percentage)						61.00%
Joint venture, total commitment						$ 266,500
Mezzanine Loan, Luxury Condominium Development Project in New York, New York | Mezzanine loans | LIBOR
Related Party Transaction [Line Items]
Loan interest rate (in percentage)						9.50%
Mezzanine Loan, Luxury Condominium Development Project in New York, New York | Loans and preferred equity held for investment | Mezzanine loans
Related Party Transaction [Line Items]
Loan carrying value						$ 20,000
Mixed-use project | Core
Related Party Transaction [Line Items]
Payments of protective advances to senior mortgage lender			7,000	$ 28,500							28,500
Impairment of investments											89,300
Mezzanine loan | LA hospitality, retail, and condominium
Related Party Transaction [Line Items]
Loans and preferred equity held for investment, net																$ 189,000
Mezzanine loan | Investment in mezzanine loan
Related Party Transaction [Line Items]
Mezzanine loan investment										$ 60,000
Mezzanine loan										$ 180,000
Joint venture commitment																	$ 101,800
Interest in joint venture (in percentage)																	31.80%
Fixed interest rate																	13.00%
Unfunded commitment remaining			14,500								14,500		14,500
Mezzanine loan | Upsized Mezzanine Loan with Affiliate
Related Party Transaction [Line Items]
Joint venture commitment												101,800		101,800
Interest in joint venture (in percentage)																45.20%
Fixed interest rate																13.00%
Preferred equity interests | Fixed rate
Related Party Transaction [Line Items]
Face value			118,715								118,715		$ 118,715		$ 115,384
Preferred equity debt investment fixed interest rate (in percentage)													12.50%		12.50%
Preferred equity interests | Fixed rate | Loans and preferred equity held for investment
Related Party Transaction [Line Items]
Loan carrying value			$ 118,696								$ 118,696		$ 118,696		$ 115,313
Preferred equity interests | Land site and development of office building | Fixed rate
Related Party Transaction [Line Items]
Preferred equity debt investment fixed interest rate (in percentage)							12.50%
Preferred equity interests | Land site and development of office building | Fixed rate | Loans and preferred equity held for investment
Related Party Transaction [Line Items]
Loan carrying value							$ 66,700
Preferred equity interests | Mixed-use development project in Ireland | Fixed rate
Related Party Transaction [Line Items]
Preferred equity debt investment fixed interest rate (in percentage)						15.00%
Maturity term (in years)						2 years
Management
Related Party Transaction [Line Items]
Granted (in shares)				143,000	800,000				978,946
Outstanding (in shares)			928,230								928,230		928,230
Share-based compensation expense											$ 1,500	$ 2,600	$ 1,700	$ 4,300
Affiliated Entity
Related Party Transaction [Line Items]
Purchase of Class A office campus							326,800
Carrying value							$ 197,700
Affiliated Entity | July 2018 Senior Mortgage Private Bond
Related Party Transaction [Line Items]
Fixed interest rate							3.91%
Initial debt term (in years)							5 years
Affiliated Entity | Land site and development of office building
Related Party Transaction [Line Items]
Interest in joint venture (in percentage)							50.00%
Affiliated Entity | Mixed-use development project in Ireland
Related Party Transaction [Line Items]
Interest in joint venture (in percentage)						39.00%
Affiliated Entity | Mezzanine loan | Investment in mezzanine loan
Related Party Transaction [Line Items]
Interest in joint venture (in percentage)																	68.20%
Affiliated Entity | Preferred equity investment
Related Party Transaction [Line Items]
Interest in joint venture (in percentage)								27.20%
Face value								$ 89,100
Preferred equity debt investment fixed interest rate (in percentage)								12.00%
Affiliated Entity | Preferred equity investment | Subsequent event
Related Party Transaction [Line Items]
Impairment of investments		$ 20,900

[1] Net of $52.5 million and $272.6 million of allowance for loan losses at June 30, 2020 and December 31, 2019, respectively. See Note 3, “Loans and Preferred Equity Held for Investments, net and Loans Held for Sale” for further details.