SCHEDULE II-VALUATION AND QUALIFYING ACCOUNTS (Details) - Allowance for Doubtful Accounts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
VALUATION AND QUALIFYING ACCOUNTS
Balance at Beginning of Period	$ 14,600	$ 13,636	$ 14,094
Charged to Costs and Expenses	10,455	11,257	10,113
Net (Deductions) Recoveries	(10,349)	(10,293)	(10,571)
Balance at End of Period	$ 14,706	$ 14,600	$ 13,636