Summary of Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($) credit_facility loan $ / shares	Jun. 30, 2021 USD ($) $ / shares	Jun. 30, 2022 USD ($) credit_facility loan $ / shares	Jun. 30, 2021 USD ($) $ / shares	Mar. 31, 2022 USD ($)	Jan. 01, 2022 USD ($)	Dec. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Apr. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Joint venture capital contribution percentage										85.00%
Borrower escrows	$ 623,300		$ 623,300				$ 531,200
CECL reserve	133,024	$ 128,945	133,024	$ 128,945	$ 122,221		124,679	$ 172,100	$ 173,549
Principal balance	24,831,546		24,831,546				22,003,017
Decrease to additional paid-in capital	(5,440,364)		(5,440,364)				(5,373,029)
Decrease to accumulated deficit	$ (811,554)		$ (811,554)				$ (794,832)
Decrease to diluted earnings per share (in dollars per share) | $ / shares	$ (0.54)	$ (0.89)	$ (1.12)	$ (1.44)
Credit Spread Option | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan	43		43
Number of credit facilities | credit_facility	8		8
Average compounded SOFR (percentage)	1.69%		1.69%
Credit Spread Option | United State Dollar LIBOR Rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average compounded SOFR (percentage)	1.79%		1.79%
Level 3 | Measurement Input, Cap Rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Measurement input (percentage)	0.0480		0.0480
Level 3 | Measurement Input, Discount Rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Measurement input (percentage)	0.0830		0.0830
Level 3 | Fair Value, Nonrecurring
Accounts, Notes, Loans and Financing Receivable [Line Items]
CECL reserve	$ 54,900		$ 54,900
Principal balance	$ 286,300		$ 286,300
Accounting Standards Update 2020-06 | Cumulative Effect, Period of Adoption, Adjustment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Decrease to additional paid-in capital						$ 2,400
Decrease to accumulated deficit						2,000
Increase to convertible notes, net						$ 476
Decrease to diluted earnings per share (in dollars per share) | $ / shares			$ 0.02
Walker and Dunlop
Accounts, Notes, Loans and Financing Receivable [Line Items]
Joint venture capital contribution percentage										15.00%