Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Parenthetical) (Detail)	Sep. 30, 2021	Dec. 31, 2020
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Percentage of Portfolio	100.00%	100.00%
Prepayment Restrictions Including Yield Maintenance Lock Out Provisions [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Percentage of Portfolio	44.00%	31.00%
Without Prepayment Restrictions [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Percentage of Portfolio	56.00%	69.00%
Floating Rate Mortgage [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Percentage of Portfolio	99.60%	99.40%
Fixed Rate Mortgage [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Percentage of Portfolio	0.40%