Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Equity Method Investments and Variable Interest Entities (Details)

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Summary of Significant Accounting Policies - Equity Method Investments and Variable Interest Entities (Details)
$ in Thousands
1 Months Ended 3 Months Ended 12 Months Ended
May 31, 2010
USD ($)
Sep. 30, 2015
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2016
USD ($)
Sep. 30, 2015
USD ($)
Schedule of Equity Method Investments [Line Items]          
Limited partner equity interest (as a percent) (at least)     50.00%    
Net investment income (loss)     $ (148) $ 0 $ 2
Share of distributions   $ 675 324 171  
Interest and Investment, Net          
Schedule of Equity Method Investments [Line Items]          
Net investment income (loss)   $ 57 $ (202) $ (103)  
Magnolia          
Schedule of Equity Method Investments [Line Items]          
Limited partner equity interest (as a percent) (at least) 39.00%        
Investment amount $ 12,150        
Minimum percentage of certificate face amount 0.05        
Acquisition fee (as a percent) 0.01