Annual report pursuant to Section 13 and 15(d)

Borrowings - Fair Value (Narrative) (Details)

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Borrowings - Fair Value (Narrative) (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Long-term line of credit $ 10,000 $ 16,550
Term Notes | Long-term mortgage notes and bonds payable    
Debt Instrument [Line Items]    
Long-term debt, fair value 284,800  
Secured debt 293,000  
Term Notes | Short Term Mortgage Notes And Bonds Payable    
Debt Instrument [Line Items]    
Long-term line of credit $ 10,000