Loans Receivable, Net - Activity Relating to Loans Receivable Portfolio (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 10,056,732
Loan contributed to securitization	512,002
Unrealized (loss) gain on foreign currency translation	(44,317)	$ 47,124	$ (49,686)
Amortization of fees and other items	47,093	38,373	40,345
Ending Balance	14,191,200	10,056,732
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	10,056,732	8,692,978
Loan fundings	7,890,051	4,072,786
Loan repayments	(3,035,383)	(2,828,610)
Loan contributed to securitization	512,002
Unrealized (loss) gain on foreign currency translation	(150,654)	136,646
Deferred fees and other items	(104,408)	(55,441)
Amortization of fees and other items	46,864	38,373
Ending Balance	14,191,200	10,056,732	8,692,978
Deferred Fees/Other Items [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	(51,494)	(34,240)
Loan contributed to securitization	5,498
Unrealized (loss) gain on foreign currency translation	770	(186)
Deferred fees and other items	(104,408)	(55,441)
Amortization of fees and other items	46,864	38,373
Ending Balance	(102,770)	(51,494)	(34,240)
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	10,108,226	8,727,218
Loan fundings	7,890,051	4,072,786
Loan repayments	(3,035,383)	(2,828,610)
Loan contributed to securitization	517,500
Unrealized (loss) gain on foreign currency translation	(151,424)	136,832
Ending Balance	$ 14,293,970	$ 10,108,226	$ 8,727,218