Summary of Significant Accounting Policies - Schedule of 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
Balance at beginning of year	$ 425	$ 477	$ 811
Provision and reserve adjustments	285	2	(152)
Write-offs less recoveries	(323)	(54)	(182)
Balance at end of year	$ 387	$ 425	$ 477