Summary of Significant Accounting Policies - Revenue Recognition - Condensed Statement of Cash flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Cash flows from operating activities
Net loss	$ (7,876)	$ (11,273)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable	(1,391)	(524)
Inventory	170	(1,584)
Deferred income on shipments to distributors	(39)	$ (237)
Deferred income on shipments to distributors			$ 1,720
ASU 2014-09 | Balances without the adoption of Topic 606
Cash flows from operating activities
Net loss	(9,204)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable	(532)
Inventory	169
Deferred income on shipments to distributors	431
Deferred income on shipments to distributors	2,151
ASU 2014-09 | Adjustments
Cash flows from operating activities
Net loss	(1,328)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable	859
Inventory	(1)
Deferred income on shipments to distributors	470
Deferred income on shipments to distributors	$ 2,151