Stock-Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock based compensation expense
Stock-based compensation expense	$ 3,154	$ 2,543
Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	142	131
Research and development
Stock based compensation expense
Stock-based compensation expense	903	650
Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 2,109	1,762
Employee and non-employee stock options
Stock based compensation expense
Options granted (in shares)	1,150,000
Unrecognized compensation expense	$ 28,000
Unrecognized compensation expense recognized over weighted average period	2 years 10 months 10 days
Employee stock options
Stock based compensation expense
Stock-based compensation expense	$ 3,149	2,557
Employee stock options | Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	138	143
Employee stock options | Research and development
Stock based compensation expense
Stock-based compensation expense	903	650
Employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 2,108	1,764
Non-employee stock options
Stock based compensation expense
Options granted (in shares)	105,448
Options unvested (in shares)	7,301
Stock-based compensation expense	$ 5	(14)
Non-employee stock options | Cost of product revenues
Stock based compensation expense
Stock-based compensation expense	4	(12)
Non-employee stock options | Selling, general and administrative
Stock based compensation expense
Stock-based compensation expense	$ 1	$ (2)