Supplemental Information - Schedule of 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 period	$ 2,591	$ 2,138	$ 1,887
Bad debt expense	1,480	1,089	268
Write-offs, net of recoveries	(219)	(635)	(8)
Effect of foreign currency translation	1	(1)	(9)
Balance at end of period	$ 3,853	$ 2,591	$ 2,138