Stock-Based Compensation - Stock-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
Schedule of stock-based compensation expense
Stock-based compensation	$ 1,770	$ 1,833	$ 6,207	$ 5,212
Stock options [Member]
Schedule of stock-based compensation expense
Stock-based compensation	472	393	1,482	1,107
RSAs and RSUs [Member]
Schedule of stock-based compensation expense
Stock-based compensation	416	456	1,293	1,399
Performance Stock Units (PSUs) [Member]
Schedule of stock-based compensation expense
Stock-based compensation	407	385	1,251	1,373
Performance Based Options (PBOs) [Member]
Schedule of stock-based compensation expense
Stock-based compensation	475	599	2,181	1,333
Research and development [Member]
Schedule of stock-based compensation expense
Stock-based compensation	552	386	1,555	1,050
Selling, General and Administrative Expenses [Member]
Schedule of stock-based compensation expense
Stock-based compensation	$ 1,218	$ 1,447	$ 4,652	$ 4,162