SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) - Allowance for doubtful accounts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Fiscal Period	$ 1,246	$ 1,751	$ 2,121
Charges to Costs and Expense	1,049	1,093	1,354
Deductions	(808)	(1,598)	(1,724)
Balance at End of Fiscal Period	$ 1,487	$ 1,246	$ 1,751