SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Loans Held-for-Investment, Net and Agency Loan Repurchases (Detail) $ in Thousands	1 Months Ended		3 Months Ended			9 Months Ended		12 Months Ended
	Nov. 07, 2024 USD ($) loan	Mar. 31, 2024 USD ($)	Sep. 30, 2024 USD ($) loan	Mar. 31, 2024 USD ($) loan	Sep. 30, 2023 USD ($) loan	Sep. 30, 2024 USD ($) loan	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) loan
Loans Held-for-Investment, Net
Unpaid principal balance of loans held for investment			$ 38,000			$ 38,000		$ 40,100
Number of delinquent loans | loan			0			0		0
Number of loans on nonaccrual status | loan			0			0		0
Amortized cost of loans held for investment, current			$ 38,000			$ 38,000		$ 40,100
Agency loan repurchases
Provision for estimated indemnification loss on agency loan to be repurchased			2,850		$ 421	$ 6,310	$ (11,088)
Maximum
Loans Held-for-Investment, Net
Loan term (in years)						3 years		3 years
Fannie Mae DUS program
Loans Held-for-Investment, Net
Financing receivable allowance for credit loss			$ 2,000			$ 2,000
Agency loan repurchases
Unpaid principal balance of loans repurchased from agency program		$ 17,900		$ 17,900
Payments to repurchase agency loans				$ 13,500				$ 4,400
Number of agency loans requested to be repurchased | loan	2
Number of agency loans classified as defaulted | loan					2
Unpaid principal balance of loans expected to be repurchased from agency program	$ 25,600
Freddie Mac
Agency loan repurchases
Number of agency loans requested to be repurchased | loan				2
Freddie Mac Loan One
Agency loan repurchases
Unpaid principal balance of loans repurchased from agency program		$ 11,400		$ 11,400
Extended period of time for the repurchase of the agency loan		6 months	6 months
Freddie Mac Loan Two
Agency loan repurchases
Unpaid principal balance of loans repurchased from agency program		$ 34,800		$ 34,800
Extended period of time for the repurchase of the agency loan		12 months
Freddie Mac Loan Two | Other Liabilities
Agency loan repurchases
Fair value of indemnification on agency loan to be repurchased			$ 7,600			$ 7,600