Stock-based Compensation - Non-cash Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Non-cash stock-based compensation expense	$ 4,183	$ 2,465	$ 6,810	$ 3,807
Cost of goods sold
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Non-cash stock-based compensation expense	716	394	976	536
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Non-cash stock-based compensation expense	886	442	1,410	917
Selling, general and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Non-cash stock-based compensation expense	$ 2,581	$ 1,629	$ 4,424	$ 2,354