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Equity Award Plan Activities (Tables)

12 Months Ended

Dec. 31, 2017

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

The following table summarizes the option activity under our stock plans and related information (in thousands, except years and per share amounts):



	Options Outstanding
	Number of Shares Underlying Outstanding Options		Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (Years) of Stock Options	Aggregate Intrinsic Value of Stock Options Outstanding
Balance—December 31, 2016	9,509		$	28.79	6.9	$	646,394
Options granted	170		96.60
Options exercised	(2,260	)	19.73
Options canceled or expired	(395	)	34.04
Balance—December 31, 2017	7,024		$	33.05	6.1	$	1,422,637
Vested and exercisable—December 31, 2017	2,992		$	20.70	5.4	$	643,012
Vested and expected to vest—December 31, 2017	7,024		$	33.05	6.1	$	1,422,637

Schedule of Restricted Stock Units Activity

A summary of the activity under our 2014 Plan and changes during the reporting period and a summary of information related to RSUs are presented below (in thousands, except years and per share 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	712		141.97
RSUs vested	(456	)	77.33
RSUs forfeited/canceled	(94	)	80.58
Unvested balance—December 31, 2017	1,537		$	104.29	1.6	$	362,119

Schedule of Shares Available for Grant

The following table presents the stock activity and the total number of shares available for grant as of December 31, 2017 (in thousands):



	Number of Shares
Balance—December 31, 2016	11,754
Authorized	2,124
Options granted	(170	)
RSUs granted	(712	)
Options canceled, expired or repurchased	399
RSUs forfeited	94
Shares traded for taxes	23
Balance—December 31, 2017	13,512

Schedule of Stock-Based Compensation Expense

Total stock-based compensation expense related to options, RSAs, ESPP and RSUs granted were charged to the department to which the associated employee reported as follow (in thousands):



	Year Ended December 31,
	2017		2016		2015
Cost of revenue	$	4,353	$	3,620	$	3,048
Research and development	42,184		31,892		25,515
Sales and marketing	17,953		15,666		11,454
General and administrative	10,937		7,854		5,286
Total stock-based compensation	$	75,427	$	59,032	$	45,303

Schedule of Stock Option Valuation Assumptions

For the years ended December 31, 2017, 2016 and 2015, the fair value of each stock option granted under our plans was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions:



	Year Ended December 31,
	2017		2016		2015
Expected term (in years)	6.3		6.7		6.2
Risk-free interest rate	2.1	%	1.5	%	1.6	%
Expected volatility	38.9	%	38.9	%	42.9	%
Dividend rate	—	%	—	%	—	%

Schedule of ESPP Valuation Assumptions

The following table summarizes the assumptions relating to our ESPP:



	Year Ended December 31,
	2017		2016		2015
Expected term (in years)	1.2		1.2		1.4
Risk-free interest rate	1.1	%	0.6	%	0.3	%
Expected volatility	31.7	%	31.8	%	34.8	%
Dividend rate	—	%	—	%	—	%