Share-Based Compensation - Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Total share-based compensation expense	$ 2,899	$ 2,260	$ 5,468	$ 3,767
Employee stock options
Total share-based compensation expense	12	268	12	547
Restricted stock units
Total share-based compensation expense	2,887	1,992	5,456	3,220
Cost of goods sold
Total share-based compensation expense	211	134	388	212
Research and development.
Total share-based compensation expense	676	441	1,252	706
Sales and marketing.
Total share-based compensation expense	260	169	488	249
General and administrative.
Total share-based compensation expense	$ 1,752	$ 1,516	$ 3,340	$ 2,600