Loans Receivable, Net - Activity Relating to Loans Receivable Portfolio (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance		$ 14,191,200
Loan repayments and sales proceeds		(4,974,881)	$ (3,035,383)	$ (2,828,610)
Loan contributed to securitization			512,002
Unrealized gain (loss) on foreign currency translation		23,920	(44,317)	47,124
Amortization of fees and other items		57,926	47,093	38,373
Ending Balance		16,400,000
Ending Balance		16,164,801	14,191,200
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance		14,191,200	10,056,732
Loan fundings		6,890,249	7,890,051
Loans repayments			(3,035,383)
Loan repayments and sales proceeds		(4,974,881)
Loan contributed to securitization			(512,002)
Unrealized gain (loss) on foreign currency translation		67,376	(150,654)
Deferred fees and other items		(66,558)	(104,408)
Amortization of fees and other items		57,415	46,864
Ending Balance		16,164,801	14,191,200	10,056,732
Deferred Fees/Other Items [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance		(102,770)	(51,494)
Loan contributed to securitization			5,498
Unrealized gain (loss) on foreign currency translation		(629)	770
Deferred fees and other items		(66,558)	(104,408)
Amortization of fees and other items		57,415	46,864
Ending Balance		(112,542)	(102,770)	(51,494)
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance		14,293,970	10,108,226
Loan fundings		6,890,249	7,890,051
Loans repayments			(3,035,383)
Loan repayments and sales proceeds		(4,974,881)
Loan contributed to securitization	$ 517,500		(517,500)
Unrealized gain (loss) on foreign currency translation		68,005	(151,424)
Ending Balance		16,277,343	$ 14,293,970	$ 10,108,226
Ending Balance		$ 16,164,801