Net Income per Share - 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								12 Months Ended
	Jan. 31, 2021	Oct. 31, 2020	Jul. 31, 2020	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2019
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Weighted average shares used in computing net income per share, basic (in shares)									150,666	147,796	144,244
Net income per share, basic (in usd per share)	$ 0.68	$ 0.64	$ 0.62	$ 0.58	$ 0.44	$ 0.56	$ 0.54	$ 0.50	$ 2.52	$ 2.04	$ 1.59
Reallocation as a result of conversion of Class B to Class A common stock:
Weighted average shares used in computing net income per share, diluted (in shares)									160,732	158,296	156,117
Net income per share, diluted (in usd per share)	$ 0.64	$ 0.60	$ 0.58	$ 0.54	$ 0.42	$ 0.52	$ 0.50	$ 0.47	$ 2.36	$ 1.90	$ 1.47
Class A common stock
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income, basic									$ 341,866	$ 266,104	$ 194,607
Weighted average shares used in computing net income per share, basic (in shares)									135,547	130,610	122,137
Net income per share, basic (in usd per share)									$ 2.52	$ 2.04	$ 1.59
Net income, basic									$ 341,866	$ 266,104	$ 194,607
Reallocation as a result of conversion of Class B to Class A common stock:
Net income, basic									38,132	35,014	35,225
Reallocation of net income to Class B common stock									0	0	0
Net income, diluted									$ 379,998	$ 301,118	$ 229,832
Conversion of Class B to Class A common stock (in shares)									15,119	17,186	22,107
Effect of potentially dilutive common shares (in shares)									10,066	10,500	11,873
Weighted average shares used in computing net income per share, diluted (in shares)									160,732	158,296	156,117
Net income per share, diluted (in usd per share)									$ 2.36	$ 1.90	$ 1.47
Class B common stock
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income, basic									$ 38,132	$ 35,014	$ 35,225
Weighted average shares used in computing net income per share, basic (in shares)									15,119	17,186	22,107
Net income per share, basic (in usd per share)									$ 2.52	$ 2.04	$ 1.59
Net income, basic									$ 38,132	$ 35,014	$ 35,225
Reallocation as a result of conversion of Class B to Class A common stock:
Net income, basic									0	0	0
Reallocation of net income to Class B common stock									21,409	17,652	14,800
Net income, diluted									$ 59,541	$ 52,666	$ 50,025
Conversion of Class B to Class A common stock (in shares)									0	0	0
Effect of potentially dilutive common shares (in shares)									10,066	10,500	11,873
Weighted average shares used in computing net income per share, diluted (in shares)									25,185	27,686	33,980
Net income per share, diluted (in usd per share)									$ 2.36	$ 1.90	$ 1.47