Equity Award Plans

We have operated under our 2013 Equity Incentive Plan ("2013 Plan") since our initial public offering ("IPO") in September 2013. Our 2013 Plan provides for the issuance of restricted stock and the granting of options, stock appreciation rights, performance shares, performance units and restricted stock units to our employees, officers, directors and consultants. Awards granted under the 2013 Plan vest over the periods determined by the Board of Directors or compensation committee of the Board of Directors, generally four years, and stock options granted under the 2013 Plan expire no more than ten years after the date of grant. In the case of an incentive stock option granted to an employee who at the time of grant owns stock representing more than 10% of the total combined voting power of all classes of stock, the exercise price shall be no less than 110% of the fair value per share on the date of grant, and the award shall expire five years from the date of grant. For options granted to any other employee, the per share exercise price shall be no less than 100% of the fair value per share on the date of grant. In the case of non-statutory stock options and options granted to consultants, the per share exercise price shall be no less than 100% of the fair value per share on the date of grant. Stock that is purchased prior to vesting is subject to our right of repurchase at any time following termination of the participant's service for so long as such stock remains unvested. Approximately 10.1 million shares and 7.2 million shares of our common stock were reserved for future grants as of March 31, 2016 and December 31, 2015, respectively, under the 2013 Plan.

Our 2013 Employee Stock Purchase Plan ("ESPP") allows eligible employees to acquire shares of our common stock at 85% of the lower of the fair market value of our common stock on the first trading day of each offering period or on the exercise date. Our ESPP provides for annual increases in the number of shares available for issuance on the first day of each fiscal year. An aggregate of 4,830,720 shares and 3,214,287 shares of common stock were available for future issuance as of March 31, 2016 and December 31, 2015, respectively, under our ESPP.

From time to time, we also grant restricted common stock or restricted stock awards outside of our equity incentive plans to certain employees in connection with acquisitions.

Stock Option Activity

A summary of the activity for our stock option changes during the reporting period and a summary of information related to options vested and options exercisable are presented below (in thousands, except per share amounts and contractual life years):



	Options Outstanding
	Number of Shares		Weighted- Average Exercise Price		Weighted- Average Grant Date Fair Value (per share)		Weighted- Average Contractual Life (years)	Aggregate Intrinsic Value
Balance — December 31, 2015	11,494		$	10.67			6.9	$	149,157
Granted	—		—		$	—
Exercised	(601	)	4.73					7,063
Cancelled	(266	)	16.99
Balance — March 31, 2016	10,627		$	10.84			6.5	$	110,382
Options exercisable — March 31, 2016	7,466		$	9.28			6.2	$	84,211

Restricted Stock Award (RSA) and Restricted Stock Unit (RSU) Activity

A summary of the activity for our restricted common stock, RSAs and RSUs during the reporting period and a summary of information related to unvested restricted common stock, RSAs and RSUs and those expected to vest based on the achievement of a performance condition are presented below (in thousands, except per share amounts and contractual life years):



	Number of Shares		Weighted- Average Grant Date Fair Value (per share)		Weighted- Average Contractual Life (years)	Aggregate Intrinsic Value
Unvested balance — December 31, 2015	20,054		$	33.68	1.6	$	415,912
Granted	6,496		12.56
Vested	(1,475	)	40.45
Cancelled	(1,179	)	34.29
Unvested balance — March 31, 2016	23,896		$	26.82	1.6	$	429,886
Unvested awards for which the requisite service period has not been rendered but that are expected to vest based on the achievement of a performance condition — March 31, 2016	7,030		$	21.49	1.6	$	126,465

Included in the approximately 6.5 million shares granted in the table above are 3.6 million shares granted to employees in connection with acquisitions.

Stock-Based Compensation

We record stock-based compensation based on the fair value of stock options on grant date using the Black-Scholes option-pricing model. We determine the fair value of shares of common stock to be issued under the ESPP using the Black-Scholes option-pricing model. The fair value of restricted stock units and restricted stock awards equals the market value of the underlying stock on the date of grant. We grant performance-based restricted stock units and restricted stock awards to certain employees which vest upon the achievement of certain performance conditions, subject to the employees’ continued service relationship with us. We assess the probability of vesting at each reporting period and adjust our compensation cost based on this probability assessment. We recognize such compensation expense on a straight-line basis over the service provider’s requisite service period.

Stock-based compensation expense related to stock options, ESPP and restricted stock units and awards is included in the condensed consolidated statements of operations as follows (in thousands):



	Three Months Ended March 31,
	2016		2015
Cost of product revenue	$	667	$	268
Cost of subscription and services revenue	9,601		6,378
Research and development	24,430		16,035
Sales and marketing	16,154		16,454
General and administrative	13,215		10,740
Total	$	64,067	$	49,875

As of March 31, 2016, total compensation cost related to stock-based awards not yet recognized was $527.7 million, which is expected to be amortized on a straight-line basis over the weighted-average remaining vesting period of approximately three years.