Schedule IV - Reconciliation of Mortgage Loans on Real Estate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Abstract]
Balance at January 1,	$ 14,191,200	$ 10,056,732	$ 8,692,978
Additions during period:
Loan fundings	6,890,249	7,890,051	4,072,786
Amortization of fees and other items	57,415	46,864	38,373
Deductions during period:
Loan repayments and sales proceeds	(4,974,881)	(3,035,383)	(2,828,610)
Loan contributed to securitization		(512,002)
Unrealized gain (loss) on foreign currency translation	67,376	(150,654)	136,646
Deferred fees and other items	(66,558)	(104,408)	(55,441)
Loans sold
Balance at December 31,	$ 16,164,801	$ 14,191,200	$ 10,056,732