Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of stock-based compensation expense
Stock-based compensation	$ 1,980	$ 1,669
Stock options [Member]
Schedule of stock-based compensation expense
Stock-based compensation	472	334
RSAs and RSUs [Member]
Schedule of stock-based compensation expense
Stock-based compensation	452	459
Performance Stock Units (PSUs) [Member]
Schedule of stock-based compensation expense
Stock-based compensation	409	641
Performance Based Options (PBOs) [Member]
Schedule of stock-based compensation expense
Stock-based compensation	647	235
Research and development [Member]
Schedule of stock-based compensation expense
Stock-based compensation	435	323
Selling, General and Administrative Expenses [Member]
Schedule of stock-based compensation expense
Stock-based compensation	$ 1,545	$ 1,346