Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) SecurityLoan	Dec. 31, 2019 USD ($) SecurityLoan	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	120	128
Principal balance	$ 16,652,824	$ 16,277,343	$ 14,293,970
Net book value	16,399,166	16,164,801	14,191,200
Unfunded loan commitments	$ 16,572,715	$ 16,164,801	$ 14,191,200	$ 10,056,732
Loans Receivable [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	120	128
Principal balance	$ 16,652,824	$ 16,277,343
Net book value	16,399,166	$ 16,164,801
Unfunded loan commitments	$ 16,572,715
Weighted-average maximum maturity (years)	3 years 1 month 6 days	3 years 9 months 18 days
Loans Receivable [Member] | Unfunded Loan Commitment [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Unfunded loan commitments	$ 3,160,084	$ 3,911,868
Loans Receivable [Member] | LIBOR [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Weighted-average cash coupon, rate description	L + 3.18	L + 3.20
Weighted-average all-in yield, rate description	L + 3.53	L + 3.55