Summary of Significant Accounting Policies - Revenue Recognition - Condensed Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Summary of Significant Accounting Policies
Accumulated deficit	$ (130,513)	$ (117,539)
Current assets:
Accounts receivable, net	5,582	4,041
Inventory	9,482	9,837
Total current assets	46,938	27,418
Total assets	51,449	31,437
Current liabilities:
Deferred income on shipments to distributors		1,720
Total current liabilities	15,907	12,375
Total liabilities	23,835	20,553
Stockholders' equity:
Accumulated deficit	(130,513)	(117,539)
Total liabilities and stockholders' equity	51,449	31,437
ASU 2014-09 | Balances without the adoption of Topic 606
Summary of Significant Accounting Policies
Accumulated deficit	(134,002)
Current assets:
Accounts receivable, net	4,952
Inventory	9,540
Total current assets	46,366
Total assets	50,877
Current liabilities:
Deferred income on shipments to distributors	2,917
Total current liabilities	18,824
Total liabilities	26,752
Stockholders' equity:
Accumulated deficit	(134,002)
Total liabilities and stockholders' equity	50,877
ASU 2014-09 | Adjustments
Summary of Significant Accounting Policies
Accumulated deficit	(3,489)	1,300
Current assets:
Accounts receivable, net	(630)
Inventory	58
Total current assets	(572)
Total assets	(572)
Current liabilities:
Deferred income on shipments to distributors	2,917
Total current liabilities	2,917
Total liabilities	2,917
Stockholders' equity:
Accumulated deficit	(3,489)	$ 1,300
Total liabilities and stockholders' equity	$ (572)