Loans Receivable, Net - Activity Relating to Loans Receivable Portfolio (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 8,692,978
Unrealized (loss) gain on foreign currency translation	47,124	$ (49,686)	$ (41,616)
Amortization of fees and other items	38,373	40,345	36,053
Ending Balance	10,056,732	8,692,978
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	8,692,978	9,077,007
Loan fundings	4,072,786	3,151,882
Loan repayments	(2,828,610)	(3,374,622)
Unrealized (loss) gain on foreign currency translation	136,646	(156,937)
Deferred fees and other items	(55,441)	(44,697)
Amortization of fees and other items	38,373	40,345
Ending Balance	10,056,732	8,692,978	9,077,007
Deferred Fees/Other Items [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	(34,240)	(31,354)
Unrealized (loss) gain on foreign currency translation	(186)	1,466
Deferred fees and other items	(55,441)	(44,697)
Amortization of fees and other items	38,373	40,345
Ending Balance	(51,494)	(34,240)	(31,354)
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	8,727,218	9,108,361
Loan fundings	4,072,786	3,151,882
Loan repayments	(2,828,610)	(3,374,622)
Unrealized (loss) gain on foreign currency translation	136,832	(158,403)
Ending Balance	$ 10,108,226	$ 8,727,218	$ 9,108,361