Loans on Watchlist or Considered to be Impaired (Detail) - USD ($) $ in Thousands	Jun. 30, 2015		Mar. 31, 2015	Dec. 31, 2014		Jun. 30, 2014	Apr. 14, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Impaired loans	$ 1,524,159			$ 1,409,254
Allowance for losses	12,796		$ 10,797	9,218		$ 15,336	$ 14,279	$ 22,955
Watchlist
Financing Receivable, Impaired [Line Items]
Impaired loans expecting full recovery	47,716			67,839
Impaired loans with reserves	43,351			13,281
Impaired loans	91,067	[1]		81,120	[2]
Commercial mortgages
Financing Receivable, Impaired [Line Items]
Impaired loans	1,282,154	[3]		1,148,290	[4]
Commercial mortgages | Watchlist
Financing Receivable, Impaired [Line Items]
Impaired loans expecting full recovery	34,920			22,920
Impaired loans	34,920	[1]		22,920	[2]
Mezzanine Loans
Financing Receivable, Impaired [Line Items]
Impaired loans	202,694			226,105
Allowance for losses	11,470		9,471	7,892		14,017	12,960	21,636
Mezzanine Loans | Watchlist
Financing Receivable, Impaired [Line Items]
Impaired loans expecting full recovery	8,500			40,559
Impaired loans with reserves	39,701			9,631
Impaired loans	48,201	[1]		50,190	[2]
Preferred Equity Interests
Financing Receivable, Impaired [Line Items]
Impaired loans	39,311			34,859
Allowance for losses	1,326		$ 1,326	1,326		$ 1,319	$ 1,319	$ 1,319
Preferred Equity Interests | Watchlist
Financing Receivable, Impaired [Line Items]
Impaired loans expecting full recovery	4,296			4,360
Impaired loans with reserves	3,650			3,650
Impaired loans	$ 7,946	[1]		$ 8,010	[2]

[1] As of June 30, 2015, this includes $5,500 of unpaid principal relating to previously identified troubled debt restructurings (TDRs) that are on accrual status.

[2] As of December 31, 2014, this includes $5,500 of unpaid principal relating to previously identified TDRs that are on accrual status.

[3] Commercial mortgages includes eleven conduit loans with an unpaid principal balance and carrying amount of $114,048 a weighted-average coupon of 4.3% and maturity dates ranging from November 2022 through July 2025. These commercial mortgages are accounted for as loans held for sale.

[4] Commercial mortgages includes 11 conduit loans with an unpaid principal balance and carrying amount of $93,925, a weighted-average coupon of 4.6% and maturity dates ranging from November 2019 through January 2025. These commercial mortgages are accounted for as loans held for sale.