Stockholders' Equity (Tables)

6 Months Ended

Jul. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

A summary of stock option activity for the six months ended July 31, 2018 is as follows:

						Weighted
				Weighted		average
				average		remaining		Aggregate
	Number			exercise		contractual		intrinsic
	of shares			price		term (in years)		value
Options outstanding at January 31, 2018		16,024,146		$	16.76		6.1	$	738,648,507
Options granted		175,000			77.88
Options exercised		(1,412,949	)		10.17
Options forfeited/cancelled		(202,268	)		8.53
Options outstanding at July 31, 2018		14,583,929		$	18.25		5.8	$	837,197,633
Options vested and exercisable at July 31, 2018		6,444,160		$	5.18		4.5	$	453,984,350
Options vested and exercisable at July 31, 2018 and expected to vest thereafter		14,583,929		$	18.25		5.8	$	837,197,633

Summary of Restricted Stock Unit (RSU) Activity

A summary of restricted stock unit (RSU) activity for the six months ended July 31, 2018 is as follows:

	Unreleased restricted			Weighted average grant
	stock units			date fair value
Balance at January 31, 2018		2,901,736		$	38.14
RSUs granted		832,014			72.02
RSUs vested		(662,087	)		36.17
RSUs forfeited/cancelled		(156,241	)		43.95
Balance at July 31, 2018		2,915,422		$	47.95

Schedule of Weighted-Average Assumptions Used to Estimate Grant Date Fair Value of Options Granted

The following table presents the weighted-average assumptions used to estimate the grant date fair value of options granted during the periods presented:

	Three Months Ended July 31,			Six Months Ended July 31,
	2018⁽¹⁾	2017		2018		2017
Volatility	—%	43%		41%		43% – 44%
Expected term (in years)	—		6.35		6.35		6.35
Risk-free interest rate	—%	1.89%		2.73%		1.89% – 2.17%
Dividend yield	—%	—%		—%		—%

⁽¹⁾Note that we did not grant any stock options during the three months ended July 31, 2018.