Loan Participations Sold, Net - Summary of Statistics for Loan Participations Sold (Parenthetical) (Detail) $ in Thousands, £ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2017 GBP (£)
Participating Mortgage Loans [Line Items]
Guarantor obligations	$ 30,100	$ 29,600		£ 24.0
Interest paid	39,287		$ 38,121
Deferred financing costs	15,974	15,272
Loan Participations Sold [Member]
Participating Mortgage Loans [Line Items]
Interest expense	2,600	2,900
Interest paid	2,500	2,800
Deferred financing costs	$ 1,500	$ 1,600