Loans on Watchlist or Considered to be Impaired (Detail) - USD ($) $ in Thousands	Jun. 30, 2016		Mar. 31, 2016	Dec. 31, 2015		Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable Impaired [Line Items]
Allowance for loan losses	$ 18,237		$ 18,165	$ 17,097		$ 12,796	$ 10,797	$ 9,218
Commercial mortgage loans
Financing Receivable Impaired [Line Items]
Allowance for loan losses	4,397		3,328	3,154
Mezzanine Loans
Financing Receivable Impaired [Line Items]
Allowance for loan losses	10,861		12,040	12,139		11,470	9,471	7,892
Preferred Equity Interests
Financing Receivable Impaired [Line Items]
Allowance for loan losses	2,979		$ 2,797	1,804		$ 1,326	$ 1,326	$ 1,326
Watchlist
Financing Receivable Impaired [Line Items]
Watchlist/Impaired loans expecting full recovery	74,800			77,800
Watchlist/Impaired loans with reserves	54,202			54,437
Total Watchlist/Impaired Loans	129,002	[1]		132,237	[2]
Watchlist | Commercial mortgage loans
Financing Receivable Impaired [Line Items]
Watchlist/Impaired loans expecting full recovery	74,800			74,800
Watchlist/Impaired loans with reserves	17,235			15,645
Total Watchlist/Impaired Loans	92,035	[1]		90,445	[2]
Watchlist | Mezzanine Loans
Financing Receivable Impaired [Line Items]
Watchlist/Impaired loans expecting full recovery				3,000
Watchlist/Impaired loans with reserves	29,053			30,846
Total Watchlist/Impaired Loans	29,053	[1]		33,846	[2]
Watchlist | Preferred Equity Interests
Financing Receivable Impaired [Line Items]
Watchlist/Impaired loans with reserves	7,914			7,946
Total Watchlist/Impaired Loans	$ 7,914	[1]		$ 7,946	[2]

[1] As of June 30, 2016, there was no unpaid principal relating to previously identified TDRs that are on accrual status.

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