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Commitments and Contingencies - Additional Information (Detail)
$ in Thousands
May 06, 2016
lawsuit
Jun. 30, 2017
USD ($)
Dec. 31, 2016
USD ($)
Aug. 31, 2016
lawsuit
Schedule of Equity Method Investments [Line Items]        
Number of class action lawsuits | lawsuit       2
Number of consolidated lawsuits | lawsuit 3      
Unfunded loan commitments   $ 119,813 $ 170,365  
Commercial Mortgage Loans [Member]        
Schedule of Equity Method Investments [Line Items]        
Unfunded loan commitments   119,813    
Subordinate Mortgage Loans [Member]        
Schedule of Equity Method Investments [Line Items]        
Unfunded loan commitments   $ 119,813