Summary of Significant Accounting Policies (Detail) $ in Thousands	Dec. 31, 2023 USD ($) loan	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Joint venture capital contribution percentage				85.00%
Restricted cash	$ 0	$ 0
Borrower escrows	640,600	459,600
CECL reserve	576,936	326,137	$ 124,679
Principal balance	23,787,012	25,017,880	22,003,017
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
CECL reserve	417,670	189,778	$ 54,874
Principal balance	$ 1,877,279	$ 929,111
Level 3 | Measurement Input, Cap Rate | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Measurement input (percentage)	0.0525
Level 3 | Measurement Input, Cap Rate | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Measurement input (percentage)	0.0800
Level 3 | Measurement Input, Discount Rate | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Measurement input (percentage)	0.0728
Level 3 | Measurement Input, Discount Rate | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Measurement input (percentage)	0.1100
Level 3 | Fair Value, Nonrecurring
Accounts, Notes, Loans and Financing Receivable [Line Items]
CECL reserve	$ 417,700
Number of loans accounted for under cost-recovery method, floating rate | loan	13
Principal balance	$ 1,900,000
Walker and Dunlop
Accounts, Notes, Loans and Financing Receivable [Line Items]
Joint venture capital contribution percentage				15.00%