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Unsecured Lines of Credit Narrative (Details) - USD ($)
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Line Of Credit Facility [Line Items]      
Lines of credit   $ 50,000,000 $ 50,000,000
Bankers Trust Operating [Member]      
Line Of Credit Facility [Line Items]      
Lines of credit   $ 0  
Bankers Trust Operating [Member] | Scenario, Forecast [Member]      
Line Of Credit Facility [Line Items]      
Lines of credit $ 0