Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Share-Based Compensation Expense Recognized to Statements of Operations

A summary of share-based compensation expense recognized in the Company’s consolidated statements of operations is as follows (in thousands):

	Year Ended December, 31
	2017		2016		2015
Cost of revenues	$	3,735	$	3,165	$	2,054
Research and development		9,550		7,296		5,387
Sales and marketing		16,015		10,902		7,200
General and administrative		12,760		9,477		7,447
Total share-based compensation expense	$	42,060	$	30,840	$	22,088

Summary of Share-Based Compensation Expense by Award Type

A summary of share-based compensation expense by award type is as follows (in thousands):

	Year Ended December, 31
	2017		2016		2015
Options	$	6,803	$	9,626	$	11,170
Employee stock purchase plan rights		2,177		1,737		1,365
Restricted stock units		33,080		19,477		9,553
Total share-based compensation expense	$	42,060	$	30,840	$	22,088

Summary of Stock Option Activity Plans

A summary of option activity under all of the plans at December 31, 2017 and changes during the periods then ended is presented in the following table:

						Weighted-
	Number of			Weighted-		Average		Aggregate
	Options			Average		Contractual		Intrinsic
	Outstanding			Exercise Price		Term		Value
	(in thousands)			Per Share		(in Years)		(in thousands)
Outstanding at December 31, 2014		9,158		$	8.23		7.2	$	61,367
Granted		1,881			16.35
Exercised		(2,323	)		6.82
Canceled/Forfeited		(668	)		11.42
Outstanding at December 31, 2015		8,048		$	10.27		6.2	$	107,091
Granted		547			16.53
Exercised		(962	)		10.01
Canceled/Forfeited		(249	)		15.50
Outstanding at December 31, 2016		7,384		$	10.59		5.3	$	74,065
Granted		25			23.99
Exercised		(1,722	)		10.39
Canceled/Forfeited		(401	)		16.04
Outstanding at December 31, 2017		5,286		$	10.30		4.2	$	201,480
Vested and expected to vest as of December 31, 2017		5,210		$	10.21		4.2	$	199,000
Exercisable as of December 31, 2017		4,609		$	9.41		4.1	$	179,743

Schedule of Total Intrinsic Values of Options Exercised

The total intrinsic values of options exercised during the years ended December 31, 2017, 2016, and 2015 were as follows (in thousands):

	Year Ended December 31,
	2017		2016		2015
Total intrinsic value of options exercised	$	41,184	$	10,718	$	28,336

Weighted Average Assumptions Used to Fair Value of Stock Options Granted

The weighted-average assumptions used in the option-pricing model and the resulting grant date fair value of stock options granted in the periods presented were as follows:

	Year ended December 31,
	2017			2016			2015
Expected term for employees (in years)		4.4			4.7			4.8
Expected term for non-employees (in years)		4.6			5.9			7.1
Expected volatility		44	%		47	%		48	%
Risk-free interest rate		1.78	%		1.12	%		1.22	%
Expected dividend yield		0	%		0	%		0	%
Grant date fair value of employee options	$	9.08		$	6.72		$	6.78

Summary of Assumptions Used to Value ESPP Rights Under the Black-Scholes Option-Pricing Model

The weighted-average assumptions used to value ESPP rights under the Black-Scholes-Merton option-pricing model and the resulting offering grant date fair value of ESPP rights granted in the periods presented were as follows:

	Year ended December 31,
	2017			2016			2015
Expected term (in years)		0.5			0.5			0.5
Expected volatility		34	%		41	%		42	%
Risk-free interest rate		1.20	%		0.50	%		0.25	%
Expected dividend yield		0	%		0	%		0	%
Offering grant date fair value of ESPP rights	$	9.52		$	5.29		$	5.05

Summary of RSUs Activity

The 2013 Plan provides for the issuance of RSUs to employees and consultants. RSUs issued under the 2013 Plan generally vest over four years. A summary of activity of RSUs under the 2013 Plan at December 31, 2017 and changes during the periods then ended is presented in the following table:

	Number of			Weighted-		Aggregate
	RSUs			Average		Intrinsic
	Outstanding			Grant Date Fair		Value
	(in thousands)			Value Per Share		(in thousands)
Outstanding at December 31, 2014		1,739		$	14.87	$	25,617
Granted		1,365			18.09
Released		(571	)		15.45
Canceled/Forfeited		(245	)		15.10
Outstanding at December 31, 2015		2,288		$	16.63	$	53,972
Granted		2,798			18.65
Released		(1,096	)		16.77
Canceled/Forfeited		(436	)		17.92
Outstanding at December 31, 2016		3,554		$	18.01	$	73,261
Granted		3,005			30.20
Released		(1,680	)		19.54
Canceled/Forfeited		(598	)		20.91
Outstanding at December 31, 2017		4,281		$	25.51	$	207,197