Changes in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance For Doubtful Accounts Receivable Rollforward
Balance at beginning of year	$ 321	$ 554	$ 565
Provision charged to selling, general and administrative expenses	33	66	283
Allowance resulting from acquisitions	120		52
Write-offs, net of recoveries of amounts previously reserved	(179)	(295)	(358)
Exchange rate changes	2	(4)	12
Balance at end of year	$ 297	$ 321	$ 554