Stock-Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock based compensation expense
Stock-based compensation expense	$ 3,616	$ 2,986
Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	191	147
Research and development
Stock based compensation expense
Stock-based compensation expense	1,047	943
Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	2,378	1,896
Employee and non-employee stock options
Stock based compensation expense
Options granted (in shares)			1,697,000
Stock-based compensation expense			$ 10,138	$ 8,406
Unrecognized compensation expense	28,400		$ 28,400
Unrecognized compensation expense recognized over weighted average period			2 years 6 months 29 days
Employee and non-employee stock options | Cost of product revenues
Stock based compensation expense
Stock-based compensation expense			$ 486	430
Employee and non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense			2,963	2,323
Employee and non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense			6,689	5,653
Employee stock options
Stock based compensation expense
Stock-based compensation expense	3,515	2,975	10,035	8,393
Employee stock options | Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	176	138	466	420
Employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	1,047	943	2,963	2,323
Employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 2,292	1,894	$ 6,606	5,650
Non-employee stock options
Stock based compensation expense
Options granted (in shares)			141,784
Options unvested (in shares)	47,541		47,541
Stock-based compensation expense	$ 101	11	$ 103	13
Non-employee stock options | Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	15	9	20	10
Non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 86	$ 2	$ 83	$ 3