Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Percentage of Portfolio	100.00%	100.00%
Additional loan receivable of floating rate	$ 16,572,715	$ 16,164,801	$ 14,191,200	$ 10,056,732
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	31.00%	61.00%
Without Prepayment Restrictions [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Percentage of Portfolio	69.00%	39.00%
Floating Rate Mortgage [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Percentage of Portfolio	99.00%	99.00%
Fixed Rate Mortgage [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Percentage of Portfolio	1.00%
Above Applicable Index Rate [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Additional loan receivable of floating rate	$ 13,700,000	$ 6,100,000