Schedule II - Valuation and Qualifying Accounts (Details) - Allowance for Doubtful Accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 915,000	$ 1,031,000	$ 1,004,000
Charged to Costs and Expense	(344,000)	(116,000)	27,000
Deductions from Reserves	0	0	0
Balance at End of Year	$ 571,000	$ 915,000	$ 1,031,000