Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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

Schedule of Stock Based Compensation Expense

The following table summarizes the components of total stock-based compensation expense included in the Company’s consolidated statements of income for the years ended December 31, 2017, 2016 and 2015 (in thousands):

	2017			2016			2015
Cost of revenue	$	20,314		$	18,287		$	14,145
Research and development	38,864			29,739			23,927
Sales and marketing	60,246			55,407			53,542
General and administrative	44,884			41,073			35,063
Total stock-based compensation	164,308			144,506			126,677
Provision for income taxes	(56,237		)	(49,014		)	(49,033		)
Total stock-based compensation, net of taxes	$	108,071		$	95,492		$	77,644

Schedule of Assumptions Used

The grant-date fair values of the Company's RSUs with market-based vesting conditions granted during the year ended December 31, 2017 and 2016 were estimated using a Monte Carlo simulation model with the following assumptions:

	2017		2016
Expected term (in years)	3.0		3.0
Risk-free interest rate	1.4	%	0.8	%
Akamai historical share price volatility	33.2	%	34.3	%
Average volatility of peer-company share price	27.1	%	27.6	%

The grant-date fair values of awards granted under the 1999 ESPP during the years ended December 31, 2017, 2016 and 2015 were estimated using the Black-Scholes option pricing model with the following weighted-average assumptions:

	2017		2016		2015
Expected term (in years)	0.5		0.5		0.5
Risk-free interest rate	1.0	%	0.5	%	0.2	%
Expected volatility	35.8	%	36.2	%	28.0	%
Dividend yield	—	%	—	%	—	%

Schedule of Summary of Stock Option Activity

The following table summarizes stock option activity during the year ended December 31, 2017:

	Shares (in thousands)		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at January 1, 2017	874		$	35.51
Exercised	(522	)	34.68
Forfeited	(13	)	47.26
Outstanding at December 31, 2017	339		$	36.36	1.66	$	9,734
Exercisable at December 31, 2017	338		$	36.31	1.66	$	9,708
Vested or expected to vest December 31, 2017	339		$	36.35	1.66	$	9,731

Schedule Of Deferred Stock Units Activity

The following table summarizes the DSU activity for the year ended December 31, 2017:

	Units (in thousands)		Weighted Average Grant Date Fair Value
Outstanding at January 1, 2017	164		$	44.90
Granted	44		47.50
Vested and distributed	(31	)	54.97
Outstanding at December 31, 2017	177		$	43.77

Schedule of Restricted Stock Units by Type

The following table summarizes the different types of restricted stock units ("RSUs") granted by the Company during the year ended December 31, 2017 (in thousands):

	December 31, 2017
RSUs with service-based vesting conditions	3,411
RSUs with market-based vesting conditions	116
RSUs with performance-based vesting conditions	82
Total	3,609

Schedule of Restricted Stock Units Activity

The following table summarizes the RSU activity for the year ended December 31, 2017:

	Units (in thousands)		Weighted Average Grant Date Fair Value
Outstanding at January 1, 2017	5,710		$	59.51
Granted	3,609		59.60
Vested	(2,910	)	59.59
Forfeited	(566	)	46.65
Outstanding at December 31, 2017	5,843		$	59.94