Schedule II - Valuation and Qualifying Account (Details) - SEC Schedule, 12-09, Allowance, Credit Loss [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Reserve for doubtful accounts, start	$ 2,590	$ 3,139	$ 4,136
Additions charged to / recovered from expense	605	(202)	(18)
Write-offs	(560)	(428)	(999)
Other	15	81	20
Reserve for doubtful accounts, end	$ 2,650	$ 2,590	$ 3,139