Property and Equipment - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 35,889	$ 35,243
Less accumulated depreciation	(19,512)	(17,819)
Property and equipment, net	16,377	17,424
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,281	4,804
Lab and clean room equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	14,197	13,787
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	15,427	15,145
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 984	$ 1,507