Schedule II. - VALUATION AND QUALIFYING ACCOUNTS (Details) - Allowance for doubtful accounts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation and Qualifying Accounts
Balance at beginning of year	$ 263	$ 375	$ 451
Charged to cost and expenses	93	103	74
Deductions	(111)	(215)	(150)
Balance at end of year	$ 245	$ 263	$ 375