Loan Participations Sold - Summary of Statistics for Loan Participations Sold (Parenthetical) (Detail) $ in Thousands, £ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 GBP (£)	Dec. 31, 2015 USD ($)
Participating Mortgage Loans [Line Items]
Guarantor obligations	$ 31,100		$ 31,100		£ 24.0
Interest paid			123,564	$ 85,494
Deferred financing costs	15,550		15,550			$ 15,646
Loan Participations Sold [Member]
Participating Mortgage Loans [Line Items]
Interest expense	3,400	$ 5,200	10,700	14,400
Interest paid	3,200	$ 4,500	10,300	$ 13,200
Deferred financing costs	$ 1,800		$ 1,800			$ 2,000