Loans Held for Sale, at Fair Value - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum period of loans held for sale sold	45 days
Financing receivable recorded investment nonaccural status	$ 0	$ 0
Management services, servicing fees and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income on Loans held for sale	34,200,000	31,600,000	$ 30,600,000
Gains (Loss) from Mortgage Banking Activities, Net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gains (loss) recognized on change in fair value on loans held for sale	$ 5,200,000	$ 18,400,000	$ 2,200,000