Schedule IV - Reconciliation of Mortgage Loans on Real Estate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Abstract]
Balance at January 1,	$ 10,056,732	$ 8,692,978	$ 9,077,007
Additions during period:
Loan fundings	7,890,051	4,072,786	3,151,882
Amortization of deferred fees and expenses	46,864	38,373	40,345
Deductions during period:
Collections of principal	(3,035,383)	(2,828,610)	(3,351,042)
Loan contributed to securitization	(512,002)
Unrealized (loss) gain on foreign currency translation	(150,654)	136,646	(156,937)
Deferred origination fees and expenses	(104,408)	(55,441)	(44,697)
Loans sold			(23,580)
Balance at December 31,	$ 14,191,200	$ 10,056,732	$ 8,692,978