Stock-based Compensation - (Tables)

6 Months Ended

Jun. 30, 2019

Share-based Payment Arrangement [Abstract]

Schedule of non-cash stock-based compensation expense

Non-cash stock-based compensation expense (employee stock purchase plan, service-based stock options and restricted stock units) included in cost of goods sold, research and development expenses and selling, general and administrative expenses is summarized in the following table: 

	Three Months Ended June 30,				Six Months Ended June 30,
(In thousands)	2019		2018		2019		2018
Cost of goods sold	$	716	$	394	$	976	$	536
Research and development	886		442		1,410		917
Selling, general and administrative	2,581		1,629		4,424		2,354
Total non-cash stock-based compensation expense	$	4,183	$	2,465	$	6,810	$	3,807

Schedule of weighted average assumptions used to estimate fair value of each service-based stock option grant

The fair value of each service-based stock option grant for the reported periods is estimated on the date of the grant using the Black-Scholes option-pricing model using the weighted average assumptions noted in the following table.

	Six Months Ended June 30,
Service-Based Stock Options	2019		2018
Expected dividend rate	—	%	—	%
Expected stock price volatility	79.5-85.5%		82.3-88.3%
Risk-free interest rate	1.9-2.7%		2.4-2.9%
Expected life (years)	5.3-6.3		5.2-6.3