|**Investment in 111 West 57th Partners LLC (Tables)**                           | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                           
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|**Investment in 111 West 57th Partners LLC [Abstract]**                         |                                                                                                                                                                                                                                                                                                                                                                                          
|Initial Investment and Other Information Relating to the 111 West 57th Property | Amounts relating to the Company’s initial June 2013 investment and other information relating to the 111 West 57th Property follows:($ in thousands)Company’s aggregate initial investment$57,250Company’s aggregate initial membership interest %60.3%Other members and Sponsor initial investment$37,750Approximate gross square feet of project346,000                                
|($ in thousands)                                                                |                                                                                                                                                                                                                                                                                                                                                                                          
|Company’s aggregate initial investment                                          |                                                                                                                                                                                                                                                                                                                                                                                          
|Company’s aggregate initial membership interest %                               |                                                                                                                                                                                                                                                                                                                                                                                          
|Other members and Sponsor initial investment                                    |                                                                                                                                                                                                                                                                                                                                                                                          
|Approximate gross square feet of project                                        |                                                                                                                                                                                                                                                                                                                                                                                          
|Information Relating to Financing for 111 West 57th Partners                    | Information relating to the June 30, 2015 financing for 111 West 57th Partners is as follows:(in thousands)Financing obtained by 111 West 57th Partners - AIG$400,000Financing obtained by 111 West 57th Partners - Apollo$325,000Annaly CRE LLC initial mortgage and acquisition loan repaid$230,000                                                                                    
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|(in thousands)                                                                  |                                                                                                                                                                                                                                                                                                                                                                                          
|Financing obtained by 111 West 57th Partners - AIG                              |                                                                                                                                                                                                                                                                                                                                                                                          
|Financing obtained by 111 West 57th Partners - Apollo                           |                                                                                                                                                                                                                                                                                                                                                                                          
|Annaly CRE LLC initial mortgage and acquisition loan repaid                     |                                                                                                                                                                                                                                                                                                                                                                                          
|Equity Method Investments                                                       | As a result of the matters described herein, the following tables present summarized financial information for 111 West 57th Partners solely for the periods indicated.  The amounts shown represent 100% of the results of operations of 111 West 57thPartners for the date indicated below.(in thousands)Three MonthsEndedMarch 31, 2017Rental income$-Expenses31Net income (loss)$(31)
|(in thousands)                                                                  |                                                                                                                                                                                                                                                                                                                                                                                          
|Rental income                                                                   |                                                                                                                                                                                                                                                                                                                                                                                          
|Expenses                                                                        |                                                                                                                                                                                                                                                                                                                                                                                          
|Net income (loss)                                                               |                                                                                                                                                                                                                                                                                                                                                                                          

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