Schedule II - Valuation and Qualifying Account (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Movement In Valuation Allowances And Reserves Roll Forward
Reserve for doubtful accounts, start	$ 2,730	$ 2,650	$ 2,590
Additions charged to / recovered from?expense	1,618	594	605
Write-offs	(650)	(454)	(560)
Other	370	(60)	15
Reserve for doubtful accounts, end	$ 4,068	$ 2,730	$ 2,650