Basis of Presentations and Summary of Significant Accounting Policies - Accounts Receivable (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) D	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Basis of Presentations and Summary of Significant Accounting Policies
Number of business days within which accounts receivable from credit card processors are typically received | D	3
Accounts receivable, past due time period individual account reviewed for collectibility	60 days
Allowance for doubtful account activity
Balance at beginning of period	$ 27	$ 197	$ 218
Charged to costs and expenses	217	228	52
Write-offs, net of recoveries	(35)	(398)	(73)
Balance at end of period	$ 209	$ 27	$ 197