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Investment and Disposition Activities - Other Activity - Additional Information (Detail)
12 Months Ended
Sep. 10, 2014
USD ($)
Option
Dec. 31, 2015
Sep. 15, 2014
USD ($)
$ / shares
Investment And Disposition Activities [Line Items]      
Maturity date   Aug. 15, 2022  
Series D Preferred Shares of Beneficial Interest [Member]      
Investment And Disposition Activities [Line Items]      
Liquidating distribution     $ 122,821,000
Liquidating distribution per share | $ / shares     $ 25.4815
Notes Payable [Member] | KeyBank National Association [Member]      
Investment And Disposition Activities [Line Items]      
Line of credit $ 25,000,000    
Periodic interest repayment Monthly    
Extension options | Option 2    
Period of extension options 3 years    
Maturity date Mar. 10, 2015    
Notes Payable [Member] | KeyBank National Association [Member] | London Interbank Offered Rate (LIBOR) [Member]      
Investment And Disposition Activities [Line Items]      
Interest bearing loan, description of variable rate basis LIBOR plus 3%    
Line of credit interest rate 300.00%