Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) SecurityLoan	Dec. 31, 2018 USD ($) SecurityLoan	Dec. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	128	125
Principal balance	$ 16,400,000
Net book value	$ 16,164,801	$ 14,191,200
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	128	125
Principal balance	$ 16,277,343	$ 14,293,970	$ 10,108,226
Net book value	16,164,801
Unfunded loan commitments	$ 3,911,868	$ 3,405,945
Weighted-average maximum maturity (years)	3 years 9 months 18 days	3 years 10 months 24 days
Loans Receivable [Member] | LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average cash coupon, rate	3.20%
Weighted-average all-in yield, rate	3.55%	3.73%
Weighted-average cash coupon, rate description		L + 3.40
Weighted-average all-in yield, rate description	L + 3.55	L + 3.73
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 16,164,801	$ 14,191,200	$ 10,056,732