Loans Receivable, Net - Activity Relating to Loans Receivable Portfolio (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance			$ 10,056,732
Loan contributed to securitization	$ 517,500
Unrealized (loss) gain on foreign currency translation	(2,416)	$ 16,175	(26,766)	$ 43,990
Amortization of fees and other items			35,955	$ 28,887
Ending Balance	12,176,516		12,176,516
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance			10,056,732
Loan fundings			5,222,803
Loan repayments			(2,452,811)
Loan contributed to securitization			512,002
Unrealized (loss) gain on foreign currency translation			(99,937)
Deferred fees and other items			(74,111)
Amortization of fees and other items			35,842
Ending Balance	12,176,516		12,176,516
Deferred Fees/Other Items [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance			(51,494)
Loan contributed to securitization			5,498
Unrealized (loss) gain on foreign currency translation			678
Deferred fees and other items			(74,111)
Amortization of fees and other items			35,842
Ending Balance	(83,587)		(83,587)
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance			10,108,226
Loan fundings			5,222,803
Loan repayments			(2,452,811)
Loan contributed to securitization			517,500
Unrealized (loss) gain on foreign currency translation			(100,615)
Ending Balance	$ 12,260,103		$ 12,260,103