Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2017

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

The following is a summary of stock option activity under the Plans (in thousands, except share and per share amounts):



	Number of Shares		Weighted-Average Exercise Price Per Share		Weighted-Average Remaining Contractual Term (In years)	Aggregate Intrinsic Value
Outstanding at December 31, 2016	4,042,627		$	8.20	7.05	$	4,091
Granted	498,450		5.68
Exercised	(111,630	)	3.03			328
Forfeited	(215,608	)	8.60
Cancelled	(61,574	)	15.35
Outstanding at March 31, 2017	4,152,265		7.91		7.28	3,841
Exercisable at March 31, 2017	2,267,596		6.99		5.92	3,726
Vested or expected to vest at March 31, 2017	3,881,040		7.88		7.15	3,836

Schedule of estimated assumptions used to calculate weighted-average fair value of options granted

The weighted‑average fair values of stock options granted in the three month periods ended March 31, 2017 and 2016 were $3.34 per share and $4.95 per share, respectively, and were calculated using the following estimated assumptions:



	Three months ended
	March 31,
	2017			2016
Weighted-average risk-free interest rate	2.02	%		1.52	%
Expected dividend yield	—	%		—	%
Expected volatility	63	%		60	%
Expected terms	6.0		years	6.0		years

Schedule of nonvested restricted stock units activity

The following is a summary of restricted stock unit activity under the 2014 Plan (in thousands, except share and per share amounts):




	Number of Shares		Weighted-Average Grant Date Fair Value
Nonvested at December 31, 2016	272,195		5.83
Granted	249,925		5.85
Vested	—		—
Forfeited	(2,000	)	5.83
Canceled	—		—
Nonvested at March 31, 2017	520,120		5.84

Summary of stock-based compensation expense for stock options granted that was recorded in the Company's results of operations

The following table summarizes the stock-based compensation expense resulting from awards granted under stock incentive plans, including the 2014 ESPP, that was recorded in the Company’s results of operations for the periods presented (in thousands):



	Three Months Ended March 31,
	2017		2016
Cost of product revenue	$	30	$	26
Research and development	302		270
Selling, general and administrative	796		968
Total stock-based compensation expense	$	1,128	$	1,264