Share-Based Compensation - Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Total share-based compensation expense	$ 2,894	$ 2,081	$ 8,362	$ 5,849
Employee stock options
Total share-based compensation expense	12	263	12	810
Restricted stock units
Total share-based compensation expense	2,882	1,818	8,350	5,039
Cost of goods sold
Total share-based compensation expense	205	124	593	336
Research and development.
Total share-based compensation expense	624	400	1,876	1,106
Sales and marketing.
Total share-based compensation expense	181	118	669	367
General and administrative.
Total share-based compensation expense	$ 1,884	$ 1,439	$ 5,224	$ 4,040