Nature of Business and Summary of Significant Accounting Policies Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	$ 21	$ 34	$ 24
Write-offs	0	(11)	(11)
Change in provision	40	(2)	21
Balance at end of year	$ 61	$ 21	$ 34