Summary of Significant Accounting Policies - Accounts Receivable and Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Industry practice payment of receivables	20 days
Changes in the allowance for doubtful accounts [Roll Forward]
Balance at beginning of period	$ 303	$ 225	$ 206
Charges to costs and expenses	43	137	100
Deductions	(193)	(59)	(81)
Balance at end of period	$ 153	$ 303	$ 225
Product Concentration Risk | Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage	90.00%