Notes Payable and Long-Term Debt (Short-Term Debt) (Details) - USD ($)	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Short-term notes payable and current portion of long-term debt	$ 1,300,000	$ 1,800,000
Notes Payable to Banks | Unsecured Debt
Short-term Debt [Line Items]
Short-term notes payable and current portion of long-term debt	800,000	1,800,000
Notes Payable to Banks | Unsecured Debt | Notes due March 2017
Short-term Debt [Line Items]
Current borrowing capacity	$ 1,000,000
Interest rate description	WSJ
Basis spread on variable rate	0.50%
Notes Payable to Banks | Unsecured Debt | Notes due November 2017
Short-term Debt [Line Items]
Current borrowing capacity	$ 800,000
Interest rate description	WSJ
Basis spread on variable rate	0.50%
Line of Credit | Unsecured Debt
Short-term Debt [Line Items]
Short-term notes payable and current portion of long-term debt	$ 500,000	0
Interest rate description	WSJ
Basis spread on variable rate	5.00%
Line of Credit | Secured Debt
Short-term Debt [Line Items]
Short-term notes payable and current portion of long-term debt	$ 0	$ 0
Current borrowing capacity	$ 1,000,000
Interest rate description	WSJ
Basis spread on variable rate	4.50%