Loans Considered to be Impaired (Detail) - USD ($) $ in Thousands	Mar. 31, 2017		Dec. 31, 2016		Mar. 31, 2016	Dec. 31, 2015
Financing Receivable Impaired [Line Items]
Impaired loans expecting full recovery	$ 78,475		$ 32,748
Impaired loans with reserves	68,660		119,659
Total Impaired Loans	147,135	[1]	152,407	[2]
Allowance for loan losses	13,531		12,354		$ 18,165	$ 17,097
Commercial Mortgage Loans
Financing Receivable Impaired [Line Items]
Impaired loans expecting full recovery	45,727
Impaired loans with reserves	61,010		113,509
Total Impaired Loans	106,737	[1]	113,509	[2]
Allowance for loan losses	10,979		10,640		3,328	3,154
Mezzanine Loans
Financing Receivable Impaired [Line Items]
Impaired loans expecting full recovery	32,748		32,748
Impaired loans with reserves	4,000
Total Impaired Loans	36,748	[1]	32,748	[2]
Allowance for loan losses	852				12,040	12,139
Preferred Equity Interests
Financing Receivable Impaired [Line Items]
Impaired loans with reserves	3,650		6,150
Total Impaired Loans	3,650	[1]	6,150	[2]
Allowance for loan losses	$ 1,700		$ 1,714		$ 2,797	$ 1,804

[1] As of March 31, 2017, there was no unpaid principal relating to previously identified TDRs that are on accrual status.

[2] As of December 31, 2016, there was no unpaid principal relating to previously identified TDRs that are on accrual status.