Stock-Based Compensation Expense (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Stock Option Activity

The following table summarizes stock option activity for the six months ended June 30, 2018:

	Number of shares		Weighted average exercise price
Outstanding at December 31, 2017	11,967,815		$	6.73
Granted	980,000		4.11
Exercised	(204,521	)	3.80
Forfeited or Expired	(1,699,249	)	5.85
Outstanding at June 30, 2018	11,044,045		$	6.68
Vested and expected to vest at June 30, 2018	8,917,383		$	6.93
Exercisable at June 30, 2018	5,809,968		$	8.00

Summary of Restricted Share Activity

The following table summarizes restricted share activity for the six months ended June 30, 2018:

	Number of shares		Weighted average grant date fair value
Outstanding at December 31, 2017	1,884,297		$	6.39
Granted	1,523,650		4.45
Vested	(598,170	)	5.62
Forfeited	(487,267	)	4.90
Outstanding at June 30, 2018	2,322,510		$	5.63

Stock Based Compensation Expense

The following table reflects stock-based compensation expense for the three and six months ended June 30, 2018 and 2017: 

	Three months ended June 30,				Six months ended June 30,
(in thousands)	2018		2017		2018		2017
Cost of goods sold	$	25	$	28	$	43	$	88
Research and development	570		483		1,312		1,061
Selling, general and administrative	4,377		3,161		7,298		6,187
Total stock-based compensation expense	$	4,972	$	3,672	$	8,653	$	7,336