Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Summary of Significant Accounting Policies
Deferred revenue	$ 3,300	$ 2,900
Deferred cost of sales	1,100	1,100
Deferred income on shipments to distributors	$ 2,150	$ 1,827