Loans Receivable, Net - Activity Relating to Loans Receivable Portfolio (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 10,056,732
Unrealized gain (loss) on foreign currency translation	10,738	$ 7,770
Amortization of fees and other items	11,229	$ 8,808
Ending Balance	11,081,716
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	10,056,732
Loan fundings	1,978,213
Loan repayments	(952,146)
Unrealized gain (loss) on foreign currency translation	6,569
Deferred fees and other items	(18,881)
Amortization of fees and other items	11,229
Ending Balance	11,081,716
Deferred Fees/Other Items [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	(51,494)
Unrealized gain (loss) on foreign currency translation	(113)
Deferred fees and other items	(18,881)
Amortization of fees and other items	11,229
Ending Balance	(59,259)
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	10,108,226
Loan fundings	1,978,213
Loan repayments	(952,146)
Unrealized gain (loss) on foreign currency translation	6,682
Ending Balance	$ 11,140,975