Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Lease expiration date	Jan. 01, 2036
Minimum sublease rental income	$ 15,400,000
Letters of credit outstanding	74,900,000
Accrued loan loss	37,900,000	$ 32,900,000
Assets available for recourse	946,900,000
Warehouse receivables	$ 677,400,000
Letters of credit expiration date	2019-09
Guarantees total	$ 56,300,000
Commitments to investment in future real estate investment	53,700,000
Commitments to investment in unconsolidated real estate subsidiary	$ 34,700,000
Maximum [Member]
Loss Contingencies [Line Items]
Co-investments typically range	2.00%
Funded loans subject to loss sharing arrangements [Member]
Loss Contingencies [Line Items]
Funded loans unpaid principal	$ 23,200,000,000
Letters of credit outstanding	64,000,000	58,000,000
SBL Program [Member]
Loss Contingencies [Line Items]
Letters of credit outstanding	5,000,000	$ 5,000,000
Funded loans not subject to loss sharing arrangements [Member]
Loss Contingencies [Line Items]
Letters of credit outstanding	$ 69,000,000