Stockholders' Equity

Stock Option Plans

We have two stock option plans – the 2004 Equity Incentive Plan (the “2004 Plan”) and the 2012 Incentive Award Plan (the “2012 Plan”). In February 2019, our Board of Directors authorized a 4.6 million increase in the shares available for grant under the 2012 Plan.

During the three months ended March 31, 2019, we issued 1.5 million shares of our common stock upon the exercise of stock options. Of these shares, 0.8 million were issued as part of a net-share settlement of a cashless option exercise and 0.4 million were tendered to satisfy the related cost and statutory withholding requirements. During the three months ended March 31, 2018, we issued 0.5 million shares of our common stock upon the exercise of stock options.

The following table summarizes our stock-based compensation:



	Three Months Ended March 31,
	2019		2018
	(in thousands)
Stock-based compensation capitalized in inventory	$	28	$	—
Cost of sales	28		—
Research and development	1,979		1,464
Selling, general and administrative	4,689		3,490
Total stock-based compensation	$	6,724	$	4,954

Stock Repurchase Program

On August 9, 2018, we announced that our Board of Directors had approved a program to repurchase up to $100 million of our common stock (the “Stock Repurchase Program”). Unless it is terminated or suspended prior to its expiration, the Stock Repurchase Program will remain in effect until June 30, 2019 with the timing and amount of any repurchases to be determined based on market conditions, our stock price and other factors. The Stock Repurchase Program does not require us to acquire any specific number of shares and we may modify, suspended or discontinue it in our sole discretion at any time, without notice. Repurchases may be made through a variety of methods, including in the open market, in block trades, through privately negotiated transactions or accelerated share repurchase transactions or any combination of such methods.

During the three months ended March 31, 2019, we repurchased 1.2 million shares of common stock under the Stock Repurchase Program in open market transactions at an average price of $11.61 per share, for an aggregate purchase price of $13.6 million. Shares repurchased are recorded as treasury stock at cost on our consolidated balance sheet. At March 31, 2019, $62.8 million of the current authorization remained available for the repurchase of shares of our common stock.