Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2015

Stock-Based Compensation Expense

The following table presents stock-based compensation expense in the Company’s consolidated statements of operations (in thousands):

	Years ended December 31,
	2015		2014		2013
Cost of product revenue	$	213	$	128	$	74
Research and development		336		185		97
Selling, general and administrative		3,049		1,453		889
Total	$	3,598	$	1,766	$	1,060

Estimated Weighted Average Assumptions

The fair value of share-based awards granted during the years ended December 31, 2015, 2014 and 2013 were calculated using the following estimated assumptions:

	2015	2014	2013
Expected term (years)	6.6 -7.2	6.5	6.5
Volatility	50.09 - 51.89%	51.00 - 51.71%	51.39% - 53.63%
Risk-free interest rate	1.67 – 2.03%	1.88 - 2.11%	1.09% - 2.08%
Expected dividend yield	—	—	—

Summary of Option Activity

Information regarding option activity for the year ended December 31, 2015 under the Plans is summarized below:

	Options Outstanding			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (in years)		(in  thousands) Aggregate Intrinsic Value
Options outstanding at December 31, 2014		1,225,117		$	8.31
Granted		310,857			15.23
Exercised		(177,693	)		5.22
Forfeited/cancelled		(117,346	)		8.81
Options outstanding at December 31, 2015		1,240,935		$	10.44		6.42	$	22,653
Options exercisable at December 31, 2015		559,922		$	6.77		3.89	$	12,048
Vested and expected to vest at December 31, 2015 (1)		1,183,574		$	10.42		6.36	$	21,652

(1) This represents the number of vested options as of December 31, 2015 plus the number of unvested options expected to vest as of December 31, 2015 based on the unvested outstanding options at December 31, 2015 adjusted for estimated forfeiture rates of 8% for awards granted to non-executive level employees and 3% for awards granted to executive level employees.