Loans Receivable, Net - Additional Information (Detail) $ in Thousands	3 Months Ended				12 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 31, 2024 USD ($) security_loan	Mar. 31, 2024 USD ($) loan	Mar. 31, 2023 USD ($)	Mar. 31, 2024 USD ($) loan	Dec. 31, 2023 USD ($) security_loan	Dec. 31, 2023 USD ($) loan	Dec. 31, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average risk rating	3.0	3.0	3.0		3.0	3.0	3.0
Increase (decrease) in CECL reserves	$ 235,447			$ 10,454
Number of loans		173	173			178	178
Amount charged off	61,013
CECL reserve	751,370	$ 751,370	$ 751,370	336,591	$ 751,370	$ 576,936	$ 576,936	$ 326,137
Net book value	22,437,942	22,437,942	22,437,942		$ 22,437,942	23,210,076	23,210,076
Number of loan modifications | loan					7
Loans held	23,959,967	23,959,967	$ 23,959,967		$ 23,959,967	24,971,028	$ 24,971,028
4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			16				15
Loans held	3,013,626	3,013,626	$ 3,013,626		3,013,626	3,036,837	$ 3,036,837
5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			17				13
Loans held	2,451,208	2,451,208	$ 2,451,208		$ 2,451,208	1,931,373	$ 1,931,373
Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loan modifications | loan					4
Aggregate amortized cost basis of loans					$ 634,200
Percentage to aggregate loans receivable portfolio					2.70%
Payment Deferral, Loan One
Accounts, Notes, Loans and Financing Receivable [Line Items]
Extension term					1 year
Contributions to reserve account					$ 2,000
Interest rate increase					5.11%
Payment Deferral, Loan Two
Accounts, Notes, Loans and Financing Receivable [Line Items]
Exit fee percentage					4.00%
Payment Deferral, Loan Three
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate increase					2.00%
Exit fee percentage					2.00%
Payment Deferral, Loan Four
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate increase					4.00%
Exit fee percentage					3.00%
Extended Maturity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loan modifications | loan					3
Aggregate amortized cost basis of loans					$ 632,800
Percentage to aggregate loans receivable portfolio					2.70%
Extended Maturity | 4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loan modifications | loan					2
Extended Maturity | 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loan modifications | loan					2
Extended Maturity, Loan One
Accounts, Notes, Loans and Financing Receivable [Line Items]
Extension term					19 months
Contributions to reserve account					$ 4,900
Interest rate reduction					2.74%
Repayment due by borrower at maturity period					$ 2,500
Extended Maturity, Loan Two
Accounts, Notes, Loans and Financing Receivable [Line Items]
Extension term					4 years 6 months
Contributions to reserve account					$ 2,000
Interest rate increase					8.50%
Increase to loan commitment					$ 50,000
Extended Maturity, Loan Three
Accounts, Notes, Loans and Financing Receivable [Line Items]
Extension term					2 years 6 months
Unfunded Loan Commitment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in CECL reserves	(2,700)			(631)
CECL reserve	12,600	12,600	12,600	15,700	$ 12,600
Unfunded loan commitments	2,089,678	2,089,678	2,089,678		2,089,678	2,430,664	$ 2,430,664
Unfunded Loan Commitment | Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded loan commitments	10,000	10,000	10,000		10,000
Unfunded Loan Commitment | Extended Maturity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded loan commitments	39,300	39,300	$ 39,300		$ 39,300
Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			52				54
Number of loan modifications | loan					5
Loans held	9,386,225	9,386,225	$ 9,386,225		$ 9,386,225	10,072,963	$ 10,072,963
Hospitality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			22				23
Number of loan modifications | loan					2
Loans held	4,074,078	4,074,078	$ 4,074,078		$ 4,074,078	4,194,588	$ 4,194,588
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			72				73
Loans held	6,056,082	6,056,082	$ 6,056,082		6,056,082	5,997,886	$ 5,997,886
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in CECL reserves	245,942			7,480
Amount charged off	61,013
CECL reserve	602,599	602,599	$ 602,599	$ 197,258	602,599	417,670	417,670	$ 189,778
Interest income	0
Impaired loans | Seven Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			7
Interest income	16,800
Impaired loans | Seventeen Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			17
CECL reserve	602,600	602,600	$ 602,600		602,600
Cash proceeds	16,800
Net book value	2,400,000	2,400,000	$ 2,400,000		2,400,000
Impaired loans | One Loan Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			1
Net book value	138,800	138,800	$ 138,800		138,800
Impaired loans | One Loan Less Than 30 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			1
Net book value	223,400	223,400	$ 223,400		223,400
Previously Impaired Loans Resolved | Three Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			3
Cash proceeds	9,500
Joint Venture | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held	$ 614,400	$ 614,400	$ 614,400		$ 614,400	$ 612,900	$ 612,900