Loans Considered to be Impaired (Detail) - USD ($) $ in Thousands	Jun. 30, 2017		Mar. 31, 2017	Dec. 31, 2016		Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable Impaired [Line Items]
Impaired loans expecting full recovery	$ 41,225			$ 32,748
Impaired loans with reserves	115,255			119,659
Total Impaired Loans	156,480	[1]		152,407	[2]
Allowance for loan losses	23,514		$ 13,531	12,354		$ 18,237	$ 18,165	$ 17,097
Commercial Mortgage Loans
Financing Receivable Impaired [Line Items]
Impaired loans expecting full recovery	5,420
Impaired loans with reserves	99,303			113,509
Total Impaired Loans	104,723	[1]		113,509	[2]
Allowance for loan losses	12,722		10,979	10,640		4,397	3,328	3,154
Mezzanine Loans
Financing Receivable Impaired [Line Items]
Impaired loans expecting full recovery	32,748			32,748
Impaired loans with reserves	12,302
Total Impaired Loans	45,050	[1]		32,748	[2]
Allowance for loan losses	9,092		852			10,861	12,040	12,139
Preferred Equity Interests
Financing Receivable Impaired [Line Items]
Impaired loans expecting full recovery	3,057
Impaired loans with reserves	3,650			6,150
Total Impaired Loans	6,707	[1]		6,150	[2]
Allowance for loan losses	$ 1,700		$ 1,700	$ 1,714		$ 2,979	$ 2,797	$ 1,804

[1] As of June 30, 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.