Stock-based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of stock-based compensation expense
Stock-based compensation	$ 7,889	$ 7,091	$ 5,673
Stock options
Schedule of stock-based compensation expense
Stock-based compensation	1,975	1,554	1,102
RSUs and RSAs
Schedule of stock-based compensation expense
Stock-based compensation	1,770	1,888	2,043
PSUs
Schedule of stock-based compensation expense
Stock-based compensation	1,511	1,792	2,528
PBOs
Schedule of stock-based compensation expense
Stock-based compensation	2,633	1,857	0
Research and development
Schedule of stock-based compensation expense
Stock-based compensation	2,055	1,444	1,033
Selling, general and administrative
Schedule of stock-based compensation expense
Stock-based compensation	$ 5,834	$ 5,647	$ 4,640