Loans Receivable, Net - Principal Balance and Net Book Value of Loans Receivable Based on Internal Risk Ratings (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021 USD ($) SecurityLoan	Dec. 31, 2020 USD ($) SecurityLoan	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	121	120
Net Book Value	$ 17,060,102	$ 16,572,715
Total Loan Exposure	18,033,021	17,454,621
CECL reserve	(172,100)	(173,549)	$ (112,694)	$ 0
Net book value of restructured loan	$ 16,888,002	$ 16,399,166
Risk Rating 1 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	7	8
Net Book Value	$ 679,670	$ 777,163
Total Loan Exposure	$ 681,516	$ 778,283
Risk Rating 2 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	19	17
Net Book Value	$ 2,567,527	$ 2,513,848
Total Loan Exposure	$ 2,581,715	$ 2,528,835
Risk Rating 3 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	79	79
Net Book Value	$ 10,515,383	$ 9,911,914
Total Loan Exposure	$ 11,460,179	$ 10,763,496
Risk Rating 4 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	14	14
Net Book Value	$ 2,960,287	$ 3,032,593
Total Loan Exposure	$ 2,970,875	$ 3,045,309
Risk Rating 5 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	2	2
Net Book Value	$ 337,235	$ 337,197
Total Loan Exposure	$ 338,736	$ 338,698