Equity Award Plan Activities

3 Months Ended

Mar. 31, 2017

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

Equity Award Plan Activities

Equity Award Plan Activities

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,
	2017		2016
Cost of revenue	$	1,024	$	793
Research and development	9,587		7,457
Sales and marketing	3,456		3,647
General and administrative	2,372		1,463
Total stock-based compensation	$	16,439	$	13,360

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, 2016	9,509		$	28.79	6.9	$	646,394
Options granted	165		95.51
Options exercised	(882	)	15.32
Options canceled	(223	)	32.10
Outstanding—March 31, 2017	8,569		$	31.38	6.8	$	864,597
Vested and exercisable—March 31, 2017	3,144		$	16.75	6.0	$	363,194
Vested and expected to vest—March 31, 2017	8,569		$	31.38	6.8	$	864,597

As of March 31, 2017, the total unrecognized stock-based compensation expense related to unvested stock options was $90.8 million, which is expected to be recognized over a weighted-average period of 3.8 years.

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, 2016	1,375		$	74.23	1.8	$	133,081
RSUs granted	283		109.51
RSUs vested	(119	)	72.85
RSUs forfeited	(20	)	69.30
Unvested balance—March 31, 2017	1,519		$	80.97	1.8	$	200,947
Vested and expected to vest—March 31, 2017	1,519		$	80.97	1.8	$	200,947

As of March 31, 2017, there was $115.1 million of unrecognized stock-based compensation cost related to unvested RSUs. This amount is expected to be recognized over a weighted-average period of 3.5 years.

Employee Stock Purchase Plan Activities

During the three months ended March 31, 2017, we issued 99,804 shares at a weighted average purchase price of $60.03 under the 2014 Employee Stock Purchase Plan ("ESPP"). On February 6, 2016, 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, 2,500,000 shares, or such amount as determined by our board of directors. The approved increase for 2017 amounted to 708,111 shares. As of March 31, 2017, there remain 2,092,153 shares available for issuance under the ESPP. 

As of March 31, 2017, the total unrecognized stock-based compensation expense related to unvested ESPP options was $3.8 million, which is expected to be recognized over a weighted-average period of 1.4 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, 2017 (in thousands):

	Number of Shares
Balance—December 31, 2016	11,754
Authorized	2,124
Options granted	(165	)
RSUs granted	(283	)
Options canceled	223
Options repurchased	2
RSUs forfeited	20
Shares traded for taxes	5
Balance—March 31, 2017	13,680