SCHEDULE II-VALUATION AND QUALIFYING ACCOUNTS (Details) - 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	$ 2,622	$ 1,231	$ 2,685
Charged to Expense	454	2,171	1,949
(Uncollectible Accounts Written Off, Net of Recoveries)	457	(780)	(3,403)
Balance at End of Period	$ 3,534	$ 2,622	$ 1,231