Loan Participations Sold, Net - Summary of Statistics for Loan Participations Sold (Parenthetical) (Detail) $ in Thousands, £ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 GBP (£)
Participating Mortgage Loans [Line Items]
Guarantor obligations	$ 29,600	$ 35,600		£ 24.0
Interest paid	164,905	127,429	$ 55,174
Deferred financing costs	15,272	15,646
Loan Participations Sold [Member]
Participating Mortgage Loans [Line Items]
Interest expense	13,700	18,300
Interest paid	13,100	16,900
Deferred financing costs	$ 1,600	$ 2,000