Summary of Significant Accounting Policies - Revenue Recognition - Condensed Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Summary of Significant Accounting Policies
Accumulated deficit	$ (124,885)	$ (117,539)
Current assets:
Accounts receivable, net	5,097	4,041
Inventory	8,851	9,837
Total current assets	47,898	27,418
Total assets	51,564	31,437
Current liabilities:
Deferred income on shipments to distributors		1,720
Total current liabilities	15,215	12,375
Total liabilities	20,581	20,553
Stockholders' equity:
Accumulated deficit	(124,885)	(117,539)
Total liabilities and stockholders' equity	51,564	31,437
ASU 2014-09 | Balances without the adoption of Topic 606
Summary of Significant Accounting Policies
Accumulated deficit	(127,513)
Current assets:
Accounts receivable, net	4,573
Inventory	8,898
Total current assets	47,421
Total assets	51,087
Current liabilities:
Deferred income on shipments to distributors	2,151
Total current liabilities	17,366
Total liabilities	22,732
Stockholders' equity:
Accumulated deficit	(127,513)
Total liabilities and stockholders' equity	51,087
ASU 2014-09 | Adjustments
Summary of Significant Accounting Policies
Accumulated deficit	(2,628)	1,300
Current assets:
Accounts receivable, net	(524)
Inventory	47
Total current assets	(477)
Total assets	(477)
Current liabilities:
Deferred income on shipments to distributors	2,151
Total current liabilities	2,151
Total liabilities	2,151
Stockholders' equity:
Accumulated deficit	(2,628)	$ 1,300
Total liabilities and stockholders' equity	$ (477)