Stockholders’ Equity

Common Stock Repurchase Program

In February 2017, our Board of Directors authorized a program to repurchase up to $25 million of outstanding common stock to offset potential dilution from issuances of common stock under our stock-based compensation plans. The share repurchase program will expire on February 1, 2020. During the nine months ended September 30, 2017, we repurchased and retired 867,620 shares of common stock for $11.0 million and, as of September 30, 2017, $14.0 million remained available for future repurchases.

Repurchased shares are retired upon the settlement of the related trade transactions with the excess of cost over par value charged to additional paid-in capital. All repurchases were made in compliance with Rule 10b-18 under the Securities Exchange Act of 1934, as amended.

Restricted Stock Units

Restricted stock unit ("RSU") activity under our equity incentive plan was as follows:



	Units		Weighted Average Grant Date Fair Value
RSUs at December 31, 2016	3,108,560		$	8.61
Awards granted	1,615,982		13.19
Awards vested	(1,331,116	)	7.94
Awards canceled	(203,653	)	8.91
RSUs at September 30, 2017	3,189,773		$	11.15

The total fair value of RSUs vested during the nine months ended September 30, 2017 was $17.8 million.

Stock Options

Stock option activity under our equity incentive plan was as follows:



	Options Outstanding		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life in Years	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2016	2,198,031		$	9.13
Options exercised	(1,431,767	)	9.37
Options canceled	(65,308	)	13.60
Outstanding at September 30, 2017	700,956		$	8.21	3.85	$	6,056
Vested and expected to vest at September 30, 2017	700,956		$	8.21	3.85	$	6,056
Exercisable at September 30, 2017	420,022		$	8.52	3.17	$	3,497

Stock-Based Compensation

Stock-based compensation was included in our Condensed Consolidated Statements of Operations as follows (in thousands):



	Three Months Ended				Nine Months Ended
	September 30, 2017		September 24, 2016		September 30, 2017		September 24, 2016
Cost of revenues	$	894	$	674	$	2,540	$	1,712
Research and development	1,437		913		3,768		2,251
Selling, general and administrative	2,255		1,615		4,971		3,514
Total stock-based compensation	$	4,586	$	3,202	$	11,279	$	7,477

Employee Stock Purchase Plan ("ESPP")

Information related to activity under our ESPP was as follows:



	Nine Months Ended
	September 30, 2017
Shares issued	655,961
Weighted average per share purchase price	$	8.68
Weighted average per share discount from the fair value of our common stock on the date of issuance	$	4.03

Unrecognized Compensation Costs

At September 30, 2017, the unrecognized stock-based compensation was as follows (in thousands):



	Unrecognized Expense		Average Expected Recognition Period in Years
Stock options	$	667	1.33
Restricted stock units	30,975		2.30
Employee stock purchase plan	1,105		0.34
Total unrecognized stock-based compensation expense	$	32,747	2.21