Loans on Watchlist or Considered to be Impaired (Detail) - USD ($) $ in Thousands	Mar. 31, 2016		Dec. 31, 2015		Mar. 31, 2015	Dec. 31, 2014
Financing Receivable Impaired [Line Items]
Allowance for loan losses	$ 18,165		$ 17,097		$ 10,797	$ 9,218
Commercial mortgages
Financing Receivable Impaired [Line Items]
Allowance for loan losses	3,328		3,154
Mezzanine Loans
Financing Receivable Impaired [Line Items]
Allowance for loan losses	12,040		12,139		9,471	7,892
Preferred Equity Interests
Financing Receivable Impaired [Line Items]
Allowance for loan losses	2,797		1,804		$ 1,326	$ 1,326
Watchlist
Financing Receivable Impaired [Line Items]
Watchlist/Impaired loans expecting full recovery	77,800		77,800
Watchlist/Impaired loans with reserves	54,189		54,437
Total Watchlist/Impaired Loans	131,989	[1]	132,237	[2]
Watchlist | Commercial mortgages
Financing Receivable Impaired [Line Items]
Watchlist/Impaired loans expecting full recovery	74,800		74,800
Watchlist/Impaired loans with reserves	15,645		15,645
Total Watchlist/Impaired Loans	90,445	[1]	90,445	[2]
Watchlist | Mezzanine Loans
Financing Receivable Impaired [Line Items]
Watchlist/Impaired loans expecting full recovery	3,000		3,000
Watchlist/Impaired loans with reserves	30,598		30,846
Total Watchlist/Impaired Loans	33,598	[1]	33,846	[2]
Watchlist | Preferred Equity Interests
Financing Receivable Impaired [Line Items]
Watchlist/Impaired loans with reserves	7,946		7,946
Total Watchlist/Impaired Loans	$ 7,946	[1]	$ 7,946	[2]

[1] As of March 31, 2016, this includes no unpaid principal relating to previously identified TDRs that are on accrual status.

[2] As of December 31, 2015, this includes no unpaid principal relating to previously identified TDRs that are on accrual status.