Employee Benefits and Stock-based Compensation (Tables)

12 Months Ended

Jan. 31, 2016

Classification of Stock-based Compensation

The following table presents the classification of stock-based compensation for the periods indicated:

	Year Ended January 31,
	2016		2015		2014
	(in thousands)
Stock-based compensation:
Cost of revenue	$	657	$	343	$	178
Research and development		19,082		8,654		4,887
Selling, general and administrative		11,355		6,695		3,470
Total stock-based compensation	$	31,094	$	15,692	$	8,535

Weighted-Average Assumptions Used to Estimate Fair Value

The following table sets forth the weighted-average assumptions used to estimate the fair value of the stock options and employee stock purchase plan awards for the periods indicated:

	Year Ended January 31,
	2016			2015			2014
Stock Options:
Volatility		57	%		64	%		65	%
Risk-free interest rate		1.74	%		1.93	%		1.55	%
Expected term (years)	6.08			6.01				6.06
Dividend yield		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		63	%		49	%		52	%
Risk-free interest rate		0.21	%		0.07	%		0.04	%
Expected term (years)		0.5			0.5			0.5
Dividend yield		0	%		0	%		0	%

Stock Option Activities

The following table summarizes stock option activities for the periods indicated:

	Option Outstanding
										Weighted-
								Total Intrinsic		Average
						Weighted-		Value of		Remaining		Aggregate
				Weighted-		Average		options		Contractual		Intrinsic
				Average		Grant-date		Exercised		Term		Value
	Shares			Exercise Price		Fair Value		(in thousands)		(in years)		(in thousands)
Outstanding at January 31, 2013		4,344,535		$	6.07
Granted		255,520			18.14	$	10.85
Exercised		(1,160,286	)		5.96			$	18,217
Forfeited		(81,063	)		10.34
Outstanding at January 31, 2014		3,358,706			6.92
Granted		428,781			36.33	$	21.37
Exercised		(1,456,944	)		5.84			$	46,427
Forfeited		(48,634	)		13.38
Outstanding at January 31, 2015		2,281,909			13.00
Granted		179,700			71.36	$	38.81
Exercised		(567,888	)		9.11			$	37,603
Forfeited		(40,331	)		35.65
Outstanding at January 31, 2016		1,853,390		$	19.36					5.89		$	43,396
Exercisable at January 31, 2016		1,363,880		$	10.23						4.93	$	40,341
Vested and expected to vest at January 31, 2016		1,822,252		$	18.84						5.84	$	43,285

Restricted Stock and Restricted Stock Units Activities

The following table summarizes restricted stock and restricted stock units activities for the periods indicated:

				Weighted-
				Average
				Grant-Date
	Shares			Fair Value
Unvested at January 31, 2013		339,217		$	9.99
Granted		1,265,472			14.78
Vested		(174,888	)		11.91
Forfeited		(19,712	)		11.97
Unvested at January 31, 2014		1,410,089			14.02
Granted		1,111,204			38.60
Vested		(484,296	)		17.39
Forfeited		(56,549	)		19.93
Unvested at January 31, 2015		1,980,448			26.82
Granted		1,314,387			66.14
Vested		(769,779	)		27.82
Forfeited		(29,568	)		42.11
Unvested at January 31, 2016		2,495,488		$	47.04