Loans Receivable, Net - Activity Relating to Loans Receivable Portfolio (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 14,191,200
Unrealized (loss) gain on foreign currency translation	5,414	$ 10,738
Amortization of fees and other items	13,356	$ 11,229
Ending Balance	14,508,735
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	14,191,200
Loan fundings	799,326
Loan repayments	(495,492)
Unrealized (loss) gain on foreign currency translation	5,978
Deferred fees and other items	(5,501)
Amortization of fees and other items	13,224
Ending Balance	14,508,735
Deferred Fees/Other Items [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	(102,770)
Loan fundings	0
Loan repayments	0
Unrealized (loss) gain on foreign currency translation	(49)
Deferred fees and other items	(5,501)
Amortization of fees and other items	13,224
Ending Balance	(95,096)
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	14,293,970
Loan fundings	799,326
Loan repayments	(495,492)
Unrealized (loss) gain on foreign currency translation	6,027
Deferred fees and other items	0
Amortization of fees and other items	0
Ending Balance	$ 14,603,831