Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 43	$ 112
Additions Charged to Revenues and Expenses	217	75
Deductions	0	(144)
Balance at End of Period	$ 260	$ 43