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
Changes in valuation and qualifying accounts
Balance at Beginning of Period	$ 494	$ 415	$ 234
Charges to Costs and Expenses	351	34	174
Additions/(Deductions)	(342)	45	7
Balance at End of Period	503	494	415
Allowance for tax valuation
Changes in valuation and qualifying accounts
Balance at Beginning of Period	6,802	5,146	5,694
Charges to Costs and Expenses	572	1,497	(171)
Additions/(Deductions)	(831)	159	(377)
Balance at End of Period	$ 6,543	$ 6,802	$ 5,146