Net Income per Share Attributable to Common Stockholders - Numerators and Denominators of the Basic and Diluted EPS Computations for Common Stock (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Apr. 30, 2019	Apr. 30, 2018
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income	$ 73,449	$ 44,310
Weighted average shares used in computing net income per share attributable to common stockholders, basic	146,708	142,777
Net income per share attributable to common stockholders, basic	$ 0.50	$ 0.31
Reallocation as a result of conversion of Class B to Class A common stock:
Weighted average shares used in computing net income per share attributable to common stockholders, diluted	157,910	154,935
Net income per share attributable to common stockholders, diluted	$ 0.47	$ 0.29
Class A common stock [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income	$ 63,652
Net income attributable to common stockholders, basic	$ 63,652
Weighted average shares used in computing net income per share attributable to common stockholders, basic	127,139
Net income per share attributable to common stockholders, basic	$ 0.50
Net income attributable to common stockholders, basic	$ 63,652
Reallocation as a result of conversion of Class B to Class A common stock:
Net income attributable to common stockholders, basic	9,797
Net income attributable to common stockholders, diluted	$ 73,449
Conversion of Class B to Class A common stock	19,569
Effect of potentially dilutive common shares	11,202
Weighted average shares used in computing net income per share attributable to common stockholders, diluted	157,910
Net income per share attributable to common stockholders, diluted	$ 0.47
Class A common stock [Member] | As adjusted [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income		$ 36,830
Net income attributable to common stockholders, basic		$ 36,830
Weighted average shares used in computing net income per share attributable to common stockholders, basic		118,675
Net income per share attributable to common stockholders, basic		$ 0.31
Net income attributable to common stockholders, basic		$ 36,830
Reallocation as a result of conversion of Class B to Class A common stock:
Net income attributable to common stockholders, basic		7,480
Net income attributable to common stockholders, diluted		$ 44,310
Conversion of Class B to Class A common stock		24,102
Effect of potentially dilutive common shares		12,158
Weighted average shares used in computing net income per share attributable to common stockholders, diluted		154,935
Net income per share attributable to common stockholders, diluted		$ 0.29
Class B common stock [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income	$ 9,797
Net income attributable to common stockholders, basic	$ 9,797
Weighted average shares used in computing net income per share attributable to common stockholders, basic	19,569
Net income per share attributable to common stockholders, basic	$ 0.50
Net income attributable to common stockholders, basic	$ 9,797
Reallocation as a result of conversion of Class B to Class A common stock:
Reallocation of net income to Class B common stock	4,516
Net income attributable to common stockholders, diluted	$ 14,313
Effect of potentially dilutive common shares	11,202
Weighted average shares used in computing net income per share attributable to common stockholders, diluted	30,771
Net income per share attributable to common stockholders, diluted	$ 0.47
Class B common stock [Member] | As adjusted [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income		$ 7,480
Net income attributable to common stockholders, basic		$ 7,480
Weighted average shares used in computing net income per share attributable to common stockholders, basic		24,102
Net income per share attributable to common stockholders, basic		$ 0.31
Net income attributable to common stockholders, basic		$ 7,480
Reallocation as a result of conversion of Class B to Class A common stock:
Reallocation of net income to Class B common stock		2,890
Net income attributable to common stockholders, diluted		$ 10,370
Effect of potentially dilutive common shares		12,158
Weighted average shares used in computing net income per share attributable to common stockholders, diluted		36,260
Net income per share attributable to common stockholders, diluted		$ 0.29