Stock-based compensation - Stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 8,776	$ 1,436	$ 14,445	$ 5,418
Cost of Goods Sold [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	297	339	1,605	1,119
Research and Development Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	2,981	363	4,508	1,357
Selling and Marketing Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	2,352	275	3,604	1,175
General and Administrative Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 3,146	$ 459	$ 4,728	$ 1,767