Employee Benefit Plans - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock-based compensation expense	$ 3,797	$ 3,952	$ 4,097
Cost of sales
Stock-based compensation expense	354	294	386
Research and development
Stock-based compensation expense	845	867	818
Selling, general and administrative
Stock-based compensation expense	$ 2,598	$ 2,791	$ 2,893