Equity Award Plan Activities

3 Months Ended

Mar. 31, 2016

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

Total stock-based compensation expense related to options, restricted stock awards, employee stock purchases, restricted stock units and stock purchase rights granted were allocated as follows (in thousands):



	Three Months Ended March 31,
	2016		2015
Cost of revenue	$	793	$	636
Research and development	7,457		4,928
Sales and marketing	3,647		2,409
General and administrative	1,463		866
Total stock-based compensation	$	13,360	$	8,839

Stock Option Activities

The following table summarizes the option and RSA (Restricted Stock Award) activity under our equity stock plans and related information:



	Options and RSAs Outstanding
	Number of Shares Underlying Outstanding Options and RSAs (in thousands)		Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (Years) of Stock Options	Aggregate Intrinsic Value of Stock Options Outstanding (in thousands)
Outstanding—December 31, 2015	11,630		$	24.49	7.6	$	620,802
Options granted	413		56.33
Options exercised	(288	)	6.58
Options canceled	(161	)	24.34
Outstanding—March 31, 2016	11,594		$	26.08	7.5	$	440,180
Vested and exercisable—March 31, 2016	3,905		$	9.47	6.5	$	210,414
Vested and expected to vest—March 31, 2016	10,982		$	25.39	7.5	$	424,280

As of March 31, 2016, the total unrecognized stock-based compensation expense related to unvested stock options, net of expected forfeitures, was $112.1 million, which is expected to be recognized over a weighted-average period of 4.1 years.

Early Exercise of Stock Options

For the three months ended March 31, 2016, we repurchased 3,750 thousand shares of common stock at the original exercise price due to the termination of the holders of the unvested shares. As of March 31, 2016, shares held by employees and directors that were subject to repurchase were approximately 0.6 million with an aggregate price of $2.0 million.

Restricted Stock Unit (RSU) Activities

A summary of the RSU activity under our stock plans during the reporting period and a summary of information related to RSUs expected to vest are presented below (in thousands, except per share and year amounts):



	Number of Shares		Weighted- Average Grant Date Fair Value Per Share		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Unvested balance—December 31, 2015	893		$	70.14	1.9	$	69,509
RSUs granted	219		57.56
RSUs vested	(17	)	69.26
RSUs forfeited	(41	)	67.86
Unvested balance—March 31, 2016	1,054		$	67.63	1.9	$	66,495
Vested and expected to vest—March 31, 2016	987		$	67.67	1.8	$	62,254

As of March 31, 2016, there was $57.3 million of unrecognized stock-based compensation cost related to unvested RSUs, net of estimated forfeitures. This amount is expected to be recognized over a weighted-average period of 3.7 years.

Employee Stock Purchase Plan Activities

During the three months ended March 31, 2016, we issued 122,937 shares at an average purchase price of $39.76 under the 2014 Employee Stock Purchase Plan ("ESPP"). On February 17, 2015, the board authorized an increase to shares available for future issuance under the ESPP. Per the ESPP, the increase is determined based on the lesser of 1% of total shares outstanding as of the first day of each fiscal year, or January 1, 2016, 2,500,000 shares or such amount as determined by our board of directors. The approved increase amounted to 681,315 shares. As of March 31, 2016, there remain 1,617,132 shares available for issuance under the ESPP.

As of March 31, 2016, the total unrecognized stock-based compensation expense related to unvested ESPP options, net of expected forfeitures, was $3.3 million, which is expected to be recognized over a weighted-average period of 1.7 years.

Shares Available for Grant

The following table presents the stock activity and the total number of shares available for grant as of March 31, 2016 (in thousands):




	Number of Shares
Balance—December 31, 2015	10,494
Authorized	2,044
Options granted	(413	)
RSUs granted	(219	)
Options canceled	161
Options repurchased	4
RSUs forfeited	41
Balance—March 31, 2016	12,112