Securitized Debt Obligations, Net - Schedule of Information on Securitized Debt Obligations (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Interest expense on securitized debt obligations	$ 10.7	$ 9.1	$ 35.2	$ 31.8
Credit spread adjustment	0.11%		0.11%
LIBOR [Member]
Debt Instrument [Line Items]
One-month USD LIBOR	0.08%		0.08%
SOFR [Member]
Debt Instrument [Line Items]
30-day average compounded SOFR	0.05%		0.05%
Collateral Assets [Member] | Single Asset Securitization [Member]
Debt Instrument [Line Items]
Total loan amount, securitized					$ 500.0