Stock-Based Compensation - Stock-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
Schedule of stock-based compensation expense
Stock-based compensation	$ 2,457	$ 1,711	$ 4,437	$ 3,379
Stock options [Member]
Schedule of stock-based compensation expense
Stock-based compensation	535	380	1,015	714
RSAs and RSUs [Member]
Schedule of stock-based compensation expense
Stock-based compensation	436	484	878	943
Performance Stock Units (PSUs) [Member]
Schedule of stock-based compensation expense
Stock-based compensation	426	348	844	988
Performance Based Options (PBOs) [Member]
Schedule of stock-based compensation expense
Stock-based compensation	1,060	499	1,700	734
Research and development [Member]
Schedule of stock-based compensation expense
Stock-based compensation	567	342	1,003	664
Selling, General and Administrative Expenses [Member]
Schedule of stock-based compensation expense
Stock-based compensation	$ 1,890	$ 1,369	$ 3,434	$ 2,715