Stock-Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock based compensation expense
Stock-based compensation expense	$ 3,368	$ 2,877
Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	153	152
Research and development
Stock based compensation expense
Stock-based compensation expense	1,013	730
Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	2,202	1,995
Employee and non-employee stock options
Stock based compensation expense
Options granted (in shares)			1,512,000
Stock-based compensation expense			$ 6,522	$ 5,420
Unrecognized compensation expense	26,100		$ 26,100
Unrecognized compensation expense recognized over weighted average period			2 years 9 months
Employee and non-employee stock options | Cost of product revenues
Stock based compensation expense
Stock-based compensation expense			$ 295	283
Employee and non-employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense			1,916	1,380
Employee and non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense			4,311	3,757
Employee stock options
Stock based compensation expense
Stock-based compensation expense	3,371	2,861	6,520	5,418
Employee stock options | Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	152	139	290	282
Employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	1,013	730	1,916	1,380
Employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 2,206	1,992	$ 4,314	3,756
Non-employee stock options
Stock based compensation expense
Options granted (in shares)			110,113
Options unvested (in shares)	8,984		8,984
Stock-based compensation expense	$ (3)	16	$ 2	2
Non-employee stock options | Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	1	13	5	1
Non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ (4)	$ 3	$ (3)	$ 1