Changes in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance For Doubtful Accounts Receivable Rollforward
Balance at beginning of year	$ 565	$ 500	$ 282
Provision charged to selling, general and administrative expenses	283	135	285
Allowance resulting from acquisitions	52	15	5
Write-offs, net of recoveries of amounts previously reserved	(358)	(82)	(29)
Divestiture of JK Lasers			(30)
Exchange rate changes	12	(3)	(13)
Balance at end of year	$ 554	$ 565	$ 500