Stock-Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Stock based compensation expense
Stock-based compensation expense	$ 4,051	$ 3,154
Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	168	142
Research and development
Stock based compensation expense
Stock-based compensation expense	894	903
Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 2,989	2,109
Employee and non-employee stock options
Stock based compensation expense
Options granted (in shares)	1,195,000
Unrecognized compensation expense	$ 45,800
Unrecognized compensation expense recognized over weighted average period	3 years 6 months 22 days
Employee stock options
Stock based compensation expense
Stock-based compensation expense	$ 3,708	3,149
Employee stock options | Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	168	138
Employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	894	903
Employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 2,646	2,108
Non-employee stock options
Stock based compensation expense
Options granted (in shares)	122,606
Options unvested (in shares)	28,793
Stock-based compensation expense	$ 343	5
Non-employee stock options | Cost of product revenues
Stock based compensation expense
Stock-based compensation expense		4
Non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 343	$ 1