SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts
VALUATION AND QUALIFYING ACCOUNTS
Balance at the Beginning of the Period	$ 2,989	$ 2,710	$ 4,251
Charged to Costs and Expenses	235	561	(813)
Deductions from Reserve	(63)	(282)	(728)
Balance at the End of the Period	3,161	2,989	2,710
Deferred tax valuation allowance
VALUATION AND QUALIFYING ACCOUNTS
Balance at the Beginning of the Period	4,070	6,125	7,734
Charged to Costs and Expenses	3,640	535	564
Deductions from Reserve	(2,296)	(2,590)	(2,173)
Balance at the End of the Period	$ 5,414	$ 4,070	$ 6,125