Stock Incentive Plans (Tables)

6 Months Ended

Jun. 30, 2016

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

Summary of activity under the Company's stock option plans

The following table summarizes activity under the Company’s stock option plans (aggregate intrinsic value in thousands):

	Shares Available for Grant		Stock Options Outstanding		Weighted Average Exercise Price	Weighted Average Remaining Contractual Life (Years)	Aggregate Intrinsic Value
Balance—December 31, 2015	1,058,359		4,179,521		$8.03	7.50	$6,511
Additional options authorized	1,107,411		—
Granted	(1,420,050	)	1,420,050		6.17
Canceled	131,166		(124,161	)	10.80
Exercised	—		(113,266	)	2.50
Balance—June 30, 2016	876,886		5,362,144		$7.59	7.89	$2,861
Options vested and exercisable—June 30, 2016			2,381,926		$6.97	6.49	$2,791
Options vested and expected to vest—June 30, 2016			5,056,829		$7.59	7.81	$2,855

Summary of stock-based compensation expense

The following table summarizes stock-based compensation expense related to stock options and the Company's employee stock purchase plan (“ESPP”) for the three and six months ended June 30, 2016 and 2015 (in thousands of dollars):

	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2015		2016		2015
Cost of revenue	$	33	$	15	$	63	$	32
Research and development	340		342		640		595
Selling and marketing	395		321		803		590
General and administrative	909		811		1,667		1,495
Total stock-based compensation expense	$	1,677	$	1,489	$	3,173	$	2,712

Schedule of assumptions used to calculate estimated grant date fair value of stock options using the Black-Scholes option-pricing valuation model

The estimated grant-date fair value of employee stock options was calculated using the Black-Scholes option-pricing model, based on the following assumptions:

	Three Months Ended June 30,		Six Months Ended June 30,
	2016	2015	2016	2015
Weighted-average volatility	55.88 – 56.29%	59.10 – 65.28%	55.88 – 56.36%	59.10 – 68.82%
Weighted-average expected term (years)	5.50 – 6.08	5.50 – 6.08	5.50 – 6.23	5.50 – 6.08
Risk-free interest rate	1.24 – 1.37%	1.58 – 2.03%	1.24 – 1.77%	1.55 – 2.03%
Expected dividend yield	—	—	—	—

Schedule of grant date fair value of the ESPP shares was calculated using Black Scholes option

The estimated grant date fair value of shares granted under the Company's ESPP was calculated using the Black-Scholes option-pricing model, based on the following assumptions:

	Three and Six Months Ended June 30, 2016
Weighted-average volatility	67.71 – 75.72%
Weighted-average expected term (years)	0.49 – 1.00
Risk-free interest rate	0.47%
Expected dividend yield	—