Schedule II Valuation and Qualifying Accounts and Reserves Supplemental Schedule (Details) - Accounts Receivable Reserves - 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 Period	$ 2,066	$ 2,121	$ 2,040
Charged to Costs and Expenses	1,155	795	1,653
Charged to Other Accounts	(91)	39	1
Deductions	(797)	(889)	(1,573)
Balance at End of Period	$ 2,333	$ 2,066	$ 2,121