Summary of Significant Accounting Policies (Detail)	6 Months Ended			12 Months Ended
	Jun. 30, 2024 USD ($) real_estate_owned_asset	Jun. 30, 2024 USD ($) loan real_estate_owned_asset	Jun. 30, 2024 USD ($) security_loan real_estate_owned_asset	Dec. 31, 2023 USD ($) loan	Dec. 31, 2023 USD ($) security_loan	Mar. 31, 2024 USD ($)	Mar. 19, 2024 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restricted cash	$ 0	$ 0	$ 0	$ 0	$ 0
Number of REO assets classified as held for sale investment | real_estate_owned_asset	1	1	1
Borrower escrows	$ 471,300,000	$ 471,300,000	$ 471,300,000	640,600,000	640,600,000
CECL reserve	893,938,000	$ 893,938,000	$ 893,938,000	$ 576,936,000	$ 576,936,000	$ 751,370,000		$ 363,875,000	$ 336,591,000	$ 326,137,000
Number of loans		166	166	178	178
Principal balance	22,870,848,000	$ 22,870,848,000	$ 22,870,848,000	$ 23,787,012,000	$ 23,787,012,000
Real estate owned, net	$ 60,018,000	$ 60,018,000	$ 60,018,000	$ 0	$ 0
Multifamily Joint Venture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Ownership percentage											85.00%
Multifamily Joint Venture | Walker & Dunlop
Accounts, Notes, Loans and Financing Receivable [Line Items]
Minority participation in senior term facility											15.00%
Building
Accounts, Notes, Loans and Financing Receivable [Line Items]
Estimated useful lives (in years)	40 years
Leasehold Improvements
Accounts, Notes, Loans and Financing Receivable [Line Items]
Estimated useful lives (in years)	10 years
Level 3 | Measurement Input, Cap Rate | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Measurement input	0.0600	0.0600	0.0600
Level 3 | Measurement Input, Cap Rate | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Measurement input	0.0855	0.0855	0.0855
Level 3 | Measurement Input, Discount Rate | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Measurement input	0.0728	0.0728	0.0728
Level 3 | Measurement Input, Discount Rate | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Measurement input	0.1100	0.1100	0.1100
Level 3 | Fair Value, Nonrecurring
Accounts, Notes, Loans and Financing Receivable [Line Items]
CECL reserve	$ 759,400,000	$ 759,400,000	$ 759,400,000
Number of loans | loan		19
Principal balance	$ 2,900,000,000	$ 2,900,000,000	$ 2,900,000,000
Level 3 | Fair Value, Nonrecurring | Mountain View, California Office Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate owned, net							$ 60,200,000
Level 3 | Fair Value, Nonrecurring | Measurement Input, Cap Rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate acquired through foreclosure, measurement input							0.0700
Level 3 | Fair Value, Nonrecurring | Measurement Input, Discount Rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate acquired through foreclosure, measurement input							0.0950