Summary of Significant Accounting Policies - Revenue Recognition - Condensed Statement of Cash flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net loss	$ (14,274)	$ (16,719)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable	(1,876)	(527)
Inventory	309	$ (2,628)
Shipping term reversal	(39)
ASU 2014-09 | Balances without the adoption of Topic 606
Cash flows from operating activities
Net loss	(16,463)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable	(911)
Inventory	297
Shipping term reversal	1,197
ASU 2014-09 | Adjustments
Cash flows from operating activities
Net loss	(2,189)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable	965
Inventory	(12)
Shipping term reversal	$ 1,236