Loans Held for Sale, at Fair Value - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Trade and Loans Receivables Held-for-sale, Net, Not Part of Disposal Group [Abstract]
Maximum period of loans held for sale sold			45 days
Financing Receivable, Nonaccrual	$ 0		$ 0		$ 0
Interest income on loans held for sale	6,800,000	$ 14,800,000	18,900,000	$ 29,900,000
Gains (loss) recognized on change in fair value on loans held for sale	$ 2,000,000.0	$ (3,200,000)	$ 27,100,000	$ 22,500,000