Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) SecurityLoan	Dec. 31, 2019 USD ($) SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	132	128
Net book value	$ 16,250,914
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	132	128
Principal balance	$ 16,468,767	$ 16,277,343
Net book value	16,250,914	16,164,801
Unfunded loan commitments	$ 3,905,323	$ 3,911,868
Weighted-average maximum maturity (years)	3 years 8 months 12 days	3 years 9 months 18 days
Loans Receivable [Member] | LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average all-in yield, rate		3.55%
Weighted-average cash coupon, rate description	L + 3.16	L + 3.20
Weighted-average all-in yield, rate description	L + 3.51	L + 3.55