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, 2020 USD ($) SecurityLoan	Dec. 31, 2019 USD ($) SecurityLoan	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	132	128
Net book value	$ 16,363,608	$ 16,164,801
Total Loan Exposure	17,161,035	16,965,864	$ 16,164,801
CECL reserve	112,694	112,694
Net book value of restructured loan	$ 16,250,914	$ 16,164,801
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	132	128
Net book value	$ 16,363,608
CECL reserve	(112,694)
Net book value of restructured loan	16,250,914
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	16,363,608	$ 16,164,801
CECL reserve	(112,694)
Net book value of restructured loan	16,250,914
Risk Rating 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loan Exposure	$ 354,879	$ 378,427
Risk Rating 1 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	5	6
Net book value	$ 353,112
Risk Rating 1 [Member] | Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	353,112	$ 376,379
Risk Rating 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loan Exposure	$ 3,115,300	$ 3,504,972
Risk Rating 2 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	26	30
Net book value	$ 3,095,443
Risk Rating 2 [Member] | Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	3,095,443	$ 3,481,123
Risk Rating 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loan Exposure	$ 10,416,291	$ 12,912,722
Risk Rating 3 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	85	89
Net book value	$ 9,659,154
Risk Rating 3 [Member] | Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	9,659,154	$ 12,137,963
Risk Rating 4 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loan Exposure	$ 3,274,565	$ 169,743
Risk Rating 4 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	16	3
Net book value	$ 3,255,899
Risk Rating 4 [Member] | Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	3,255,899	$ 169,336
Risk Rating 5 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loan Exposure	$ 0	$ 0
Risk Rating 5 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	0	0
Risk Rating 5 [Member] | Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 0	$ 0