Loan Participations Sold, Net - Summary of Statistics for Loan Participations Sold (Parenthetical) (Detail) $ in Thousands, £ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 GBP (£)
Participating Mortgage Loans [Line Items]
Guarantor obligations	$ 31,300	$ 29,600	$ 31,300	$ 29,600		£ 24.0
Interest paid			88,519		$ 84,408
Deferred financing costs	17,729	15,272	17,729	15,272
Loan Participations Sold [Member]
Participating Mortgage Loans [Line Items]
Interest expense	2,700	2,900	5,300	6,300
Interest paid	2,600	2,800	5,000	6,000
Deferred financing costs	$ 1,400	$ 1,600	$ 1,400	$ 1,600