Loans Receivable, Net - Property Type and Geographic Distribution of Properties Securing Loans in Portfolio (Detail) $ in Thousands	Mar. 31, 2022 USD ($) SecurityLoan	Dec. 31, 2021 USD ($) SecurityLoan	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	203	188
Principal balance	$ 23,708,990	$ 22,003,017
CECL reserve	(122,221)	(124,679)	$ (172,100)	$ (173,549)
Loans receivable, net	23,586,769	21,878,338
Total Loan Exposure	$ 25,627,588	$ 23,669,111
Percentage of Portfolio	100.00%	100.00%
Total loan exposure including senior interests	$ 1,800,000	$ 1,500,000
2018 Single Asset Securitization
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan amount, securitized		$ 379,300
Subtotal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	167	156
Principal balance	$ 16,517,359	$ 15,357,571
Total Loan Exposure	$ 18,124,203	$ 16,706,378
Percentage of Portfolio	71.00%	71.00%
Sunbelt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	77	71
Principal balance	$ 6,539,286	$ 5,907,230
Total Loan Exposure	$ 6,925,148	$ 6,206,216
Percentage of Portfolio	27.00%	26.00%
Northeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	40	37
Principal balance	$ 5,064,458	$ 4,615,076
Total Loan Exposure	$ 5,386,993	$ 4,934,295
Percentage of Portfolio	21.00%	21.00%
West
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	34	33
Principal balance	$ 3,597,537	$ 3,520,942
Total Loan Exposure	$ 4,384,370	$ 4,199,208
Percentage of Portfolio	17.00%	18.00%
Midwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	10	10
Principal balance	$ 998,899	$ 1,063,202
Total Loan Exposure	$ 1,105,755	$ 1,113,959
Percentage of Portfolio	5.00%	5.00%
Northwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	6	5
Principal balance	$ 317,179	$ 251,121
Total Loan Exposure	$ 321,937	$ 252,700
Percentage of Portfolio	1.00%	1.00%
Subtotal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	36	32
Principal balance	$ 7,191,631	$ 6,645,446
Total Loan Exposure	$ 7,503,385	$ 6,962,733
Percentage of Portfolio	29.00%	29.00%
United Kingdom
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	20	17
Principal balance	$ 2,859,326	$ 2,342,146
Total Loan Exposure	$ 3,112,309	$ 2,598,033
Percentage of Portfolio	12.00%	11.00%
Spain
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	4	4
Principal balance	$ 1,332,371	$ 1,374,364
Total Loan Exposure	$ 1,338,394	$ 1,380,763
Percentage of Portfolio	5.00%	6.00%
Ireland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	2	1
Principal balance	$ 1,192,974	$ 1,210,375
Total Loan Exposure	$ 1,198,452	$ 1,216,864
Percentage of Portfolio	5.00%	5.00%
Australia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	4	4
Principal balance	$ 539,090	$ 504,668
Total Loan Exposure	$ 543,807	$ 509,885
Percentage of Portfolio	2.00%	2.00%
Sweden
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	1	1
Principal balance	$ 524,566	$ 546,319
Total Loan Exposure	$ 528,975	$ 551,149
Percentage of Portfolio	2.00%	2.00%
Canada
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	1	2
Principal balance	$ 48,317	$ 68,558
Total Loan Exposure	$ 48,443	$ 68,478
Percentage of Portfolio	0.00%	0.00%
Other Europe
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	4	3
Principal balance	$ 694,987	$ 599,016
Total Loan Exposure	$ 733,005	$ 637,561
Percentage of Portfolio	3.00%	3.00%
Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	66	65
Principal balance	$ 9,801,292	$ 9,473,039
Total Loan Exposure	$ 10,851,461	$ 10,425,026
Percentage of Portfolio	42.00%	44.00%
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	85	75
Principal balance	$ 6,529,190	$ 5,721,260
Total Loan Exposure	$ 6,584,594	$ 5,771,517
Percentage of Portfolio	26.00%	24.00%
Hospitality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	27	25
Principal balance	$ 3,894,062	$ 3,427,245
Total Loan Exposure	$ 4,009,562	$ 3,540,391
Percentage of Portfolio	16.00%	15.00%
Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	7	6
Principal balance	$ 1,205,970	$ 1,102,452
Total Loan Exposure	$ 1,290,660	$ 1,185,606
Percentage of Portfolio	5.00%	5.00%
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	9	8
Principal balance	$ 1,124,256	$ 871,241
Total Loan Exposure	$ 1,164,740	$ 909,970
Percentage of Portfolio	4.00%	4.00%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	9	9
Principal balance	$ 1,154,220	$ 1,407,780
Total Loan Exposure	$ 1,726,571	$ 1,836,601
Percentage of Portfolio	7.00%	8.00%