CRE Debt and Preferred Equity Investments (Detail) - USD ($) $ in Thousands		Jun. 30, 2017		Dec. 31, 2016		Dec. 31, 2015
Real Estate [Line Items]
Carrying Value		$ 928,181		$ 970,505	[1]	$ 1,348,817
Preferred Equity Interests
Real Estate [Line Items]
Carrying Value		8,976		8,967	[1]	121,773
Commercial Mortgage
Real Estate [Line Items]
Outstanding Principal	[1]	931,469		975,015
Carrying Value	[1],[2]	$ 928,181		$ 970,505
Percentage of Loan Portfolio	[1],[3]	100.00%		100.00%
Commercial Mortgage | Mezzanine Loans
Real Estate [Line Items]
Outstanding Principal		$ 393,810		$ 453,693
Carrying Value		$ 392,670	[2]	$ 451,467	[1],[2]	578,503
Percentage of Loan Portfolio	[3]	42.30%		46.50%
Commercial Mortgage | Senior Mortgages
Real Estate [Line Items]
Outstanding Principal		$ 528,659		$ 512,322
Carrying Value		$ 526,535	[2]	$ 510,071	[1],[2]	$ 385,838
Percentage of Loan Portfolio	[3]	56.70%		52.60%
Commercial Mortgage | Preferred Equity Interests
Real Estate [Line Items]
Outstanding Principal		$ 9,000		$ 9,000
Carrying Value	[2]	$ 8,976		$ 8,967
Percentage of Loan Portfolio	[3]	1.00%		0.90%

[1] Excludes Loans held for sale, net.

[2] Carrying value includes unamortized origination fees of $3.3 million and $4.5 million as of June 30, 2017 and December 31, 2016, respectively.

[3] Based on outstanding principal.