Changes in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance For Doubtful Accounts Receivable Rollforward
Balance at beginning of year	$ 297	$ 321	$ 554
Addition to credit loss expense	158	33	66
Credit loss resulting from acquisitions		120
Write-offs, net of recoveries of amounts previously reserved	(207)	(179)	(295)
Exchange rate changes	26	2	(4)
Balance at end of year	$ 274	$ 297	$ 321