Loans Receivable, Net - Principal Balance and Net Book Value of Loans Receivable Based on Internal Risk Ratings (Detail) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) SecurityLoan	Dec. 31, 2019 USD ($) SecurityLoan	Mar. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	128	128
Net Book Value	$ 16,339,403	$ 16,164,801
Total Loan Exposure	17,174,244	16,965,864		$ 16,164,801
CECL reserve	(178,050)	0	$ (112,694)
Net book value of restructured loan	$ 16,161,353	$ 16,164,801
Risk Rating 1 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	6	6
Net Book Value	$ 403,025	$ 376,379
Total Loan Exposure	$ 404,596	$ 378,427
Risk Rating 2 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	28	30
Net Book Value	$ 3,143,641	$ 3,481,123
Total Loan Exposure	$ 3,163,083	$ 3,504,972
Risk Rating 3 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of Loans | SecurityLoan	78	89
Net Book Value	$ 9,509,007	$ 12,137,963
Total Loan Exposure	$ 10,306,208	$ 12,912,722
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	3
Net Book Value	$ 2,951,069	$ 169,336
Total Loan Exposure	$ 2,966,195	$ 169,743
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
Net Book Value	$ 332,661
Total Loan Exposure	$ 334,162