Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Schedule of stock-based compensation expense
Stock-based compensation	$ 1,988	$ 2,457	$ 4,051	$ 4,437
Stock options [Member]
Schedule of stock-based compensation expense
Stock-based compensation	581	535	1,135	1,015
RSAs and RSUs [Member]
Schedule of stock-based compensation expense
Stock-based compensation	386	436	847	878
Performance Stock Units (PSUs) [Member]
Schedule of stock-based compensation expense
Stock-based compensation	316	426	707	844
Performance Based Options (PBOs) [Member]
Schedule of stock-based compensation expense
Stock-based compensation	705	1,060	1,362	1,700
Research and development [Member]
Schedule of stock-based compensation expense
Stock-based compensation	403	567	791	1,003
Selling, General and Administrative Expenses [Member]
Schedule of stock-based compensation expense
Stock-based compensation	$ 1,585	$ 1,890	$ 3,260	$ 3,434